/* ==========================================================================
   班笺 · 初任教师启程专属信笺 (A Letter to Teacher Chen on Her First Year of Teaching)
   全维度 3D 信封拟物拆信、金石火漆印、宣纸舒展与典雅传统书卷美学样式系统
   文件规模：超 1000+ 行专属美学细节手工精修系统
   ========================================================================== */

:root {
  /* 宣纸与岁月纸张色彩体系 */
  --letter-paper-pure: #ffffff;
  --letter-paper-base: #fbf9f4;
  --letter-paper-warm: #f6f2e8;
  --letter-paper-aged: #efe8d8;
  --letter-paper-dark: #e5dbc7;
  --letter-paper-crease: rgba(78, 56, 36, 0.08);
  --letter-paper-edge: rgba(140, 110, 80, 0.22);
  --letter-grid-line: rgba(184, 53, 34, 0.15);
  --letter-grid-double: rgba(184, 53, 34, 0.32);
  --letter-grid-faint: rgba(184, 53, 34, 0.06);
  
  /* 拟物信封皮质与复古牛皮纸色彩 */
  --envelope-leather-light: #e8e2d4;
  --envelope-leather-base: #ddd4c1;
  --envelope-leather-mid: #cbbfab;
  --envelope-leather-dark: #b8aa93;
  --envelope-leather-deep: #9e8f76;
  --envelope-leather-inner: #877760;
  --envelope-lining-cream: #f4efe4;
  --envelope-lining-pattern: rgba(171, 40, 30, 0.08);
  --envelope-shadow-ambient: rgba(22, 16, 10, 0.35);
  --envelope-shadow-drop: rgba(18, 12, 6, 0.52);
  --envelope-shadow-lift: rgba(18, 12, 6, 0.22);
  
  /* 朱砂金石火漆印色彩体系 */
  --wax-cinnabar-bright: #e64a38;
  --wax-cinnabar-base: #bf2d1f;
  --wax-cinnabar-deep: #8c1a10;
  --wax-cinnabar-dark: #5e0e07;
  --wax-cinnabar-faint: rgba(191, 45, 31, 0.12);
  --wax-gold-leaf: #d4af37;
  --wax-gold-bright: #f3e5ab;
  --wax-gold-faint: rgba(212, 175, 55, 0.35);
  --wax-shadow-glow: rgba(191, 45, 31, 0.42);
  --wax-shadow-depth: rgba(94, 14, 7, 0.65);
  
  /* 丝绸系带与传统编织色彩 */
  --ribbon-jade-base: #1b5e4b;
  --ribbon-jade-dark: #124033;
  --ribbon-jade-light: #2a856c;
  --ribbon-jade-faint: rgba(27, 94, 75, 0.12);
  --ribbon-gold-thread: #cfab57;
  
  /* 墨黑与师者书法色彩 */
  --ink-soot-black: #161c19;
  --ink-primary-wash: #2d3832;
  --ink-secondary-wash: #4a5750;
  --ink-faint-wash: #75837c;
  --ink-bleed-soft: rgba(22, 28, 25, 0.15);
  
  /* 雅金与锦缎装饰 */
  --gold-emboss-bright: #dfb75c;
  --gold-emboss-base: #b8860b;
  --gold-emboss-deep: #8a6508;
  --gold-foil-glow: rgba(223, 183, 92, 0.32);
  
  /* 动效物理曲线 */
  --ease-spring: cubic-bezier(0.175, 0.885, 0.32, 1.275);
  --ease-silk: cubic-bezier(0.25, 1, 0.5, 1);
  --ease-wax-melt: cubic-bezier(0.4, 0, 0.2, 1);
  --ease-letter-unfold: cubic-bezier(0.16, 1, 0.3, 1);
}

/* ==========================================================================
   1. 模态背景与空间氛围沉浸层 (Ambient Lighting & Stage Container)
   ========================================================================== */
.welcome-letter-backdrop {
  position: fixed;
  inset: 0;
  z-index: 2000;
  display: flex;
  align-items: center;
  justify-content: center;
  background: radial-gradient(circle at 50% 45%, rgba(36, 28, 20, 0.84) 0%, rgba(18, 14, 10, 0.94) 70%, rgba(8, 6, 4, 0.98) 100%);
  backdrop-filter: blur(22px);
  -webkit-backdrop-filter: blur(22px);
  opacity: 0;
  visibility: hidden;
  pointer-events: none;
  transition: opacity 0.5s var(--ease-silk), visibility 0.5s var(--ease-silk);
  padding: 24px;
  overflow-y: auto;
  overflow-x: hidden;
}

.welcome-letter-backdrop.is-visible {
  opacity: 1;
  visibility: visible;
  pointer-events: auto;
}

/* 墨韵与星辉氛围光晕层 (Ambient Atmospheric Glows) */
.welcome-letter-backdrop::before {
  content: "";
  position: absolute;
  top: 25%;
  left: 50%;
  transform: translate(-50%, -50%);
  width: 720px;
  height: 720px;
  background: radial-gradient(circle, rgba(27, 94, 75, 0.14) 0%, rgba(191, 45, 31, 0.08) 45%, transparent 70%);
  pointer-events: none;
  filter: blur(70px);
  animation: aura-breathe 9s infinite alternate ease-in-out;
}

.welcome-letter-backdrop::after {
  content: "";
  position: absolute;
  bottom: 15%;
  left: 45%;
  width: 500px;
  height: 500px;
  background: radial-gradient(circle, rgba(212, 175, 55, 0.08) 0%, transparent 65%);
  pointer-events: none;
  filter: blur(80px);
  animation: aura-breathe-subtle 12s infinite alternate ease-in-out;
}

@keyframes aura-breathe {
  0% { transform: translate(-50%, -50%) scale(0.92) rotate(0deg); opacity: 0.65; }
  50% { opacity: 0.9; }
  100% { transform: translate(-50%, -50%) scale(1.18) rotate(12deg); opacity: 1; }
}

@keyframes aura-breathe-subtle {
  0% { transform: translate(-50%, -50%) scale(1.1) rotate(0deg); opacity: 0.4; }
  100% { transform: translate(-50%, -50%) scale(0.85) rotate(-15deg); opacity: 0.8; }
}

/* 3D 舞台主视口 */
.welcome-letter-stage {
  position: relative;
  width: min(880px, 100%);
  min-height: 620px;
  perspective: 1800px;
  perspective-origin: 50% 45%;
  display: flex;
  align-items: center;
  justify-content: center;
}

/* 顶部优雅退出按钮 */
.welcome-close-trigger {
  position: absolute;
  top: -14px;
  right: -14px;
  width: 44px;
  height: 44px;
  border-radius: 50%;
  background: rgba(255, 255, 255, 0.92);
  border: 1.5px solid rgba(255, 255, 255, 0.65);
  color: var(--ink-secondary-wash);
  font-size: 24px;
  line-height: 1;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  box-shadow: 0 6px 20px rgba(0, 0, 0, 0.3), inset 0 1px 2px rgba(255, 255, 255, 0.8);
  z-index: 120;
  transition: all var(--duration-normal) var(--ease-spring);
}

.welcome-close-trigger:hover {
  transform: rotate(90deg) scale(1.12);
  background: #fff;
  color: var(--wax-cinnabar-base);
  border-color: var(--wax-cinnabar-bright);
  box-shadow: 0 8px 26px rgba(191, 45, 31, 0.35);
}

.welcome-close-trigger:active {
  transform: rotate(90deg) scale(0.96);
}

/* ==========================================================================
   2. 3D 信封拟物架构与立体折翼 (3D Envelope Anatomy)
   ========================================================================== */
.envelope-wrapper {
  position: relative;
  width: 540px;
  height: 350px;
  transform-style: preserve-3d;
  transition: transform 0.85s cubic-bezier(0.2, 1, 0.3, 1), opacity 0.5s ease;
}

.welcome-letter-backdrop.is-opened .envelope-wrapper {
  transform: translateY(220px) scale(0.9) rotateX(8deg);
}

/* 信封主体盒体 */
.envelope-box {
  position: relative;
  width: 100%;
  height: 100%;
  background: linear-gradient(145deg, var(--envelope-leather-light) 0%, var(--envelope-leather-base) 60%, var(--envelope-leather-mid) 100%);
  border-radius: 14px;
  box-shadow: 0 30px 70px var(--envelope-shadow-ambient), 0 8px 20px var(--envelope-shadow-drop), inset 0 1px 3px rgba(255, 255, 255, 0.6);
  transform-style: preserve-3d;
}

/* 信封皮质边缘缝线仿真 (Stitched Edge Details) */
.envelope-box::before {
  content: "";
  position: absolute;
  inset: 5px;
  border: 1px dashed rgba(158, 143, 118, 0.45);
  border-radius: 10px;
  pointer-events: none;
  z-index: 2;
}

/* 信封内衬与暗纹水印 (Interior Lining with Auspicious Watermarks) */
.envelope-interior-lining {
  position: absolute;
  inset: 8px;
  background: var(--envelope-lining-cream) url('../img/paper-texture.png') repeat;
  border-radius: 10px;
  overflow: hidden;
  box-shadow: inset 0 0 30px rgba(120, 95, 70, 0.22);
}

.envelope-lining-watermark {
  position: absolute;
  inset: 0;
  opacity: 0.08;
  background-image: 
    radial-gradient(circle at 50% 50%, var(--wax-cinnabar-base) 1px, transparent 1px),
    linear-gradient(45deg, rgba(27, 94, 75, 0.1) 25%, transparent 25%, transparent 75%, rgba(27, 94, 75, 0.1) 75%);
  background-size: 20px 20px, 40px 40px;
}

.envelope-lining-seal-faint {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  font: 700 120px/1 var(--serif);
  color: rgba(191, 45, 31, 0.05);
  pointer-events: none;
  user-select: none;
}

/* 复古邮戳印鉴 (Vintage Postal Cancellation Stamp) */
.envelope-postmark {
  position: absolute;
  top: 24px;
  right: 28px;
  width: 84px;
  height: 84px;
  border: 1.5px dashed rgba(140, 26, 16, 0.32);
  border-radius: 50%;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  transform: rotate(-12deg);
  color: rgba(140, 26, 16, 0.45);
  font-family: var(--serif);
  font-size: 10.5px;
  letter-spacing: 0.12em;
  pointer-events: none;
  user-select: none;
}

.postmark-inner-circle {
  width: 70px;
  height: 70px;
  border: 1px solid rgba(140, 26, 16, 0.25);
  border-radius: 50%;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 2px;
}

.postmark-city {
  font-weight: 700;
  font-size: 11px;
  letter-spacing: 0.14em;
}

.postmark-date {
  font-size: 9px;
  letter-spacing: 0.06em;
  font-variant-numeric: tabular-nums;
}

.postmark-star {
  font-size: 8px;
  opacity: 0.7;
}

/* 左右下三向立体折叠翼 (3-Way Envelope Pocket Assembly) */
.envelope-pocket-assembly {
  position: absolute;
  inset: 0;
  z-index: 10;
  pointer-events: none;
}

.envelope-left-fold {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  width: 52%;
  background: linear-gradient(90deg, var(--envelope-leather-dark) 0%, var(--envelope-leather-base) 100%);
  clip-path: polygon(0 0, 100% 50%, 0 100%);
  border-radius: 14px 0 0 14px;
  box-shadow: 3px 0 12px rgba(0, 0, 0, 0.12);
}

.envelope-left-fold::after {
  content: "";
  position: absolute;
  inset: 0;
  background: linear-gradient(135deg, rgba(255, 255, 255, 0.15) 0%, transparent 60%);
}

.envelope-right-fold {
  position: absolute;
  top: 0;
  bottom: 0;
  right: 0;
  width: 52%;
  background: linear-gradient(-90deg, var(--envelope-leather-dark) 0%, var(--envelope-leather-base) 100%);
  clip-path: polygon(100% 0, 0 50%, 100% 100%);
  border-radius: 0 14px 14px 0;
  box-shadow: -3px 0 12px rgba(0, 0, 0, 0.12);
}

.envelope-right-fold::after {
  content: "";
  position: absolute;
  inset: 0;
  background: linear-gradient(-135deg, rgba(255, 255, 255, 0.15) 0%, transparent 60%);
}

.envelope-bottom-fold {
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  height: 64%;
  background: linear-gradient(0deg, var(--envelope-leather-deep) 0%, var(--envelope-leather-mid) 70%, var(--envelope-leather-base) 100%);
  clip-path: polygon(0 100%, 50% 18%, 100% 100%);
  border-radius: 0 0 14px 14px;
  box-shadow: 0 -3px 14px rgba(0, 0, 0, 0.14);
}

.envelope-bottom-fold::before {
  content: "";
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  height: 40%;
  background: linear-gradient(0deg, rgba(0, 0, 0, 0.08) 0%, transparent 100%);
}

/* 信封上盖 3D 拟物翻折 (Top Flap with 3D Physics Flip) */
.envelope-top-flap {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 65%;
  background: linear-gradient(180deg, var(--envelope-leather-light) 0%, var(--envelope-leather-base) 70%, var(--envelope-leather-dark) 100%);
  clip-path: polygon(0 0, 50% 100%, 100% 0);
  transform-origin: top center;
  transform: rotateX(0deg);
  transition: transform 0.85s cubic-bezier(0.4, 0, 0.2, 1), z-index 0.42s step-end, box-shadow 0.85s ease;
  z-index: 20;
  border-radius: 14px 14px 0 0;
  box-shadow: 0 6px 18px rgba(0, 0, 0, 0.18);
}

.envelope-top-flap::after {
  content: "";
  position: absolute;
  inset: 0;
  background: linear-gradient(180deg, rgba(255, 255, 255, 0.2) 0%, transparent 60%, rgba(0, 0, 0, 0.08) 100%);
}

.welcome-letter-backdrop.is-opened .envelope-top-flap {
  transform: rotateX(180deg);
  z-index: 1;
  box-shadow: 0 -6px 18px rgba(0, 0, 0, 0.12);
}

/* 丝绸系带装饰 (Silk Ribbon & Golden Thread) */
.envelope-silk-ribbon {
  position: absolute;
  top: 50%;
  left: 0;
  right: 0;
  height: 18px;
  background: linear-gradient(180deg, var(--ribbon-jade-light) 0%, var(--ribbon-jade-base) 60%, var(--ribbon-jade-dark) 100%);
  transform: translateY(-50%);
  z-index: 15;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.25);
  display: flex;
  align-items: center;
  justify-content: center;
}

.envelope-silk-ribbon::before {
  content: "";
  position: absolute;
  top: 50%;
  left: 0;
  right: 0;
  height: 1px;
  background: var(--ribbon-gold-thread);
  opacity: 0.7;
}

.welcome-letter-backdrop.is-opened .envelope-silk-ribbon {
  opacity: 0;
  transform: translateY(-50%) scaleX(0.8);
  transition: opacity 0.4s ease, transform 0.4s ease;
}

/* ==========================================================================
   3. 朱砂金石火漆印章 (Artisanal Cinnabar Wax Seal)
   ========================================================================== */
.wax-seal {
  position: absolute;
  top: 55%;
  left: 50%;
  transform: translate(-50%, -50%);
  width: 78px;
  height: 78px;
  border-radius: 50%;
  background: radial-gradient(circle at 32% 32%, var(--wax-cinnabar-bright) 0%, var(--wax-cinnabar-base) 55%, var(--wax-cinnabar-deep) 85%, var(--wax-cinnabar-dark) 100%);
  box-shadow: 
    0 8px 24px var(--wax-shadow-depth),
    0 2px 8px var(--wax-shadow-glow),
    inset 0 2px 5px rgba(255, 255, 255, 0.45),
    inset 0 -4px 8px rgba(0, 0, 0, 0.55);
  cursor: pointer;
  z-index: 35;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: transform var(--duration-normal) var(--ease-spring), box-shadow var(--duration-normal) ease, opacity 0.45s ease;
  user-select: none;
  outline: none;
}

.wax-seal:hover {
  transform: translate(-50%, -50%) scale(1.1);
  box-shadow: 
    0 12px 32px var(--wax-shadow-depth),
    0 0 24px rgba(230, 74, 56, 0.6),
    inset 0 3px 6px rgba(255, 255, 255, 0.55);
}

.wax-seal:active {
  transform: translate(-50%, -50%) scale(0.94);
}

.wax-seal:focus-visible {
  box-shadow: 
    0 0 0 4px rgba(255, 255, 255, 0.8),
    0 0 0 8px var(--wax-cinnabar-bright),
    0 12px 32px var(--wax-shadow-depth);
}

/* 火漆融浆不规则边缘裙边 */
.wax-irregular-rim {
  position: absolute;
  inset: -5px;
  border-radius: 47% 53% 49% 51% / 53% 48% 52% 47%;
  background: radial-gradient(circle at 28% 28%, var(--wax-cinnabar-bright) 0%, var(--wax-cinnabar-base) 60%, var(--wax-cinnabar-dark) 100%);
  z-index: -1;
  box-shadow: inset 0 1px 3px rgba(255, 255, 255, 0.3), 0 3px 8px rgba(0, 0, 0, 0.3);
  transform: rotate(14deg);
}

.wax-irregular-rim-2 {
  position: absolute;
  inset: -8px;
  border-radius: 53% 47% 55% 45% / 46% 54% 46% 54%;
  background: radial-gradient(circle at 35% 35%, var(--wax-cinnabar-base) 0%, var(--wax-cinnabar-deep) 70%, var(--wax-cinnabar-dark) 100%);
  z-index: -2;
  opacity: 0.85;
  transform: rotate(-22deg);
}

/* 火漆同心浮雕金线圈 (Embossed Concentric Rings) */
.wax-embossed-ring-outer {
  width: 58px;
  height: 58px;
  border-radius: 50%;
  border: 1.5px solid rgba(255, 255, 255, 0.35);
  box-shadow: 
    inset 0 2px 4px rgba(0, 0, 0, 0.4),
    0 1px 2px rgba(255, 255, 255, 0.25);
  display: flex;
  align-items: center;
  justify-content: center;
}

.wax-embossed-ring-inner {
  width: 48px;
  height: 48px;
  border-radius: 50%;
  border: 1px dashed rgba(255, 255, 255, 0.25);
  display: flex;
  align-items: center;
  justify-content: center;
  background: radial-gradient(circle at center, rgba(230, 74, 56, 0.3) 0%, transparent 80%);
}

/* 印章中央金石大字「启」 */
.wax-seal-emblem-text {
  font: 700 25px/1 var(--serif);
  color: #fff;
  text-shadow: 
    0 2px 4px rgba(60, 8, 4, 0.7),
    0 -1px 1px rgba(255, 255, 255, 0.3),
    0 0 8px rgba(255, 255, 255, 0.2);
  letter-spacing: -0.04em;
  transform: rotate(-3deg);
}

/* 悬浮提示胶囊标签 (Pulsing Click Hint) */
.wax-seal-hover-pill {
  position: absolute;
  bottom: -32px;
  left: 50%;
  transform: translateX(-50%);
  font-size: 12px;
  font-weight: 650;
  color: var(--wax-cinnabar-deep);
  background: rgba(255, 255, 255, 0.95);
  padding: 3px 12px;
  border-radius: var(--radius-full);
  border: 1px solid rgba(191, 45, 31, 0.2);
  box-shadow: 0 4px 14px rgba(0, 0, 0, 0.18);
  white-space: nowrap;
  letter-spacing: 0.08em;
  animation: seal-pill-bounce 2.2s infinite ease-in-out;
  pointer-events: none;
}

@keyframes seal-pill-bounce {
  0%, 100% { opacity: 0.9; transform: translateX(-50%) translateY(0); }
  50% { opacity: 1; transform: translateX(-50%) translateY(-3px); box-shadow: 0 6px 18px rgba(191, 45, 31, 0.25); }
}

.welcome-letter-backdrop.is-opened .wax-seal {
  opacity: 0;
  pointer-events: none;
  transform: translate(-50%, -50%) scale(1.6) rotate(15deg);
}

/* ==========================================================================
   4. 弹出信纸与纸张全景展开 (Letter Paper Architecture)
   ========================================================================== */
.letter-paper-container {
  position: absolute;
  top: 10px;
  left: 50%;
  transform: translateX(-50%) translateY(0) scale(0.94);
  width: 92%;
  max-width: 760px;
  background: var(--letter-paper-base) url('../img/paper-texture.png') repeat;
  border-radius: 10px;
  box-shadow: 0 10px 30px rgba(0, 0, 0, 0.2);
  opacity: 0;
  visibility: hidden;
  z-index: 5;
  transition: all 0.85s cubic-bezier(0.16, 1, 0.3, 1);
  overflow: hidden;
}

.welcome-letter-backdrop.is-opened .letter-paper-container {
  opacity: 1;
  visibility: visible;
  top: -60px;
  transform: translateX(-50%) translateY(-30px) scale(1);
  box-shadow: 
    0 28px 90px rgba(0, 0, 0, 0.5),
    0 6px 20px rgba(0, 0, 0, 0.15),
    inset 0 0 80px rgba(210, 195, 170, 0.3);
  z-index: 60;
  max-height: 84vh;
  overflow-y: auto;
  scrollbar-width: thin;
}

/* 宣纸正文包裹层与古典暗纹 */
.letter-paper-body {
  padding: 56px 64px 44px;
  position: relative;
  background: radial-gradient(circle at 50% 30%, var(--letter-paper-pure) 0%, var(--letter-paper-warm) 65%, var(--letter-paper-aged) 100%);
  border: 1px solid var(--letter-paper-edge);
}

/* 乌丝栏与红格装饰边框 (Red Traditional Ruled Grid Border) */
.letter-ruled-frame {
  position: absolute;
  inset: 16px;
  border: 1.5px solid var(--letter-grid-double);
  border-radius: 4px;
  pointer-events: none;
}

.letter-ruled-frame::before {
  content: "";
  position: absolute;
  inset: 4px;
  border: 1px solid var(--letter-grid-line);
}

/* 四角如意纹 / 锦云角饰 (Corner Filigrees) */
.letter-corner-decoration {
  position: absolute;
  width: 24px;
  height: 24px;
  border: 2px solid var(--wax-cinnabar-base);
  opacity: 0.6;
}

.corner-top-left { top: 22px; left: 22px; border-right: none; border-bottom: none; }
.corner-top-right { top: 22px; right: 22px; border-left: none; border-bottom: none; }
.corner-bottom-left { bottom: 22px; left: 22px; border-right: none; border-top: none; }
.corner-bottom-right { bottom: 22px; right: 22px; border-left: none; border-top: none; }

/* 信头朱砂红双线栏 (Red Letterhead Strip) */
.letter-header-strip {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding-bottom: 18px;
  border-bottom: 2px solid var(--wax-cinnabar-base);
  position: relative;
  margin-bottom: 32px;
}

.letter-header-strip::after {
  content: "";
  position: absolute;
  bottom: -4px;
  left: 0;
  right: 0;
  height: 1px;
  background: var(--wax-cinnabar-base);
  opacity: 0.5;
}

.letter-brand-seal {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  font: 700 16px var(--serif);
  color: var(--wax-cinnabar-base);
  letter-spacing: 0.12em;
}

.letter-seal-stamp {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 30px;
  height: 30px;
  border: 1.5px solid var(--wax-cinnabar-base);
  color: var(--wax-cinnabar-base);
  border-radius: 5px;
  font: 700 15px/1 var(--serif);
  background: rgba(191, 45, 31, 0.08);
  box-shadow: 0 1px 4px rgba(191, 45, 31, 0.12);
  transform: rotate(-1deg);
}

.letter-meta-date {
  font-size: 13px;
  color: var(--ink-faint-wash);
  font-family: var(--serif);
  letter-spacing: 0.08em;
}

/* ==========================================================================
   5. 信笺抒情正文排版系统 (Letter Typography & Soulful Content)
   ========================================================================== */
.letter-salutation {
  margin: 0 0 24px;
  font: 600 clamp(22px, 2.5vw, 27px)/1.2 var(--serif);
  color: var(--ink-soot-black);
  letter-spacing: 0.06em;
  display: flex;
  align-items: center;
  gap: 10px;
}

.salutation-drop-badge {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 34px;
  height: 34px;
  border-radius: 6px;
  background: var(--wax-cinnabar-base);
  color: #fff;
  font: 700 17px/1 var(--serif);
  box-shadow: 0 2px 8px rgba(191, 45, 31, 0.25);
  margin-right: 4px;
}

.letter-article {
  display: grid;
  gap: 20px;
  color: var(--ink-primary-wash);
  font-family: var(--serif);
  font-size: 16px;
  line-height: 2.05;
  letter-spacing: 0.035em;
  text-align: justify;
}

.letter-paragraph {
  margin: 0;
  text-indent: 2.2em;
}

/* 文人名言立体引用框 (Poetic Callout Box) */
.letter-quote-callout {
  margin: 16px 0;
  padding: 20px 28px;
  background: rgba(27, 94, 75, 0.05);
  border-left: 3.5px solid var(--ribbon-jade-base);
  border-radius: 0 var(--radius) var(--radius) 0;
  color: var(--ribbon-jade-dark);
  font-size: 15.5px;
  line-height: 1.85;
  font-style: normal;
  text-indent: 0;
  box-shadow: inset 0 0 20px rgba(27, 94, 75, 0.03);
}

.letter-emphasis {
  color: var(--wax-cinnabar-base);
  font-weight: 600;
}

.letter-emphasis-jade {
  color: var(--ribbon-jade-dark);
  font-weight: 600;
}

/* 结尾落款与朱砂大印 (Signature & Red Seal Stamp) */
.letter-signature-block {
  margin-top: 40px;
  padding-top: 28px;
  border-top: 1px solid var(--letter-paper-edge);
  display: flex;
  justify-content: flex-end;
  align-items: flex-end;
  gap: 20px;
}

.signature-text-group {
  text-align: right;
  font-family: var(--serif);
}

.signature-sign-off {
  font-size: 14px;
  color: var(--ink-faint-wash);
  margin-bottom: 6px;
}

.signature-team-name {
  font-size: 17px;
  font-weight: 600;
  color: var(--ink-soot-black);
  letter-spacing: 0.08em;
}

.signature-seal-stamp {
  width: 58px;
  height: 58px;
  border: 2px solid var(--wax-cinnabar-base);
  color: var(--wax-cinnabar-base);
  border-radius: 10px;
  display: flex;
  align-items: center;
  justify-content: center;
  font: 700 14px/1.2 var(--serif);
  text-align: center;
  padding: 6px;
  background: rgba(191, 45, 31, 0.05);
  box-shadow: 0 2px 10px rgba(191, 45, 31, 0.18), inset 0 0 6px rgba(191, 45, 31, 0.08);
  transform: rotate(-3deg);
  user-select: none;
}

/* ==========================================================================
   6. 底部操作控制栏 (Footer Controls & Preferences)
   ========================================================================== */
.letter-actions-bar {
  margin-top: 36px;
  padding-top: 22px;
  border-top: 1px dashed var(--letter-paper-edge);
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 16px;
}

.letter-dismiss-option {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  font-size: 13.5px;
  color: var(--ink-faint-wash);
  cursor: pointer;
  user-select: none;
  transition: color var(--duration-fast) ease;
}

.letter-dismiss-option:hover {
  color: var(--ink-soot-black);
}

.letter-daily-note {
  margin: 0;
  cursor: default;
  text-wrap: pretty;
}

.letter-dismiss-option input[type="checkbox"] {
  width: 17px;
  height: 17px;
  accent-color: var(--wax-cinnabar-base);
  cursor: pointer;
}

.letter-buttons-group {
  display: flex;
  align-items: center;
  gap: 12px;
}

.letter-primary-btn {
  padding: 10px 26px;
  border-radius: var(--radius-sm);
  background: var(--ribbon-jade-base);
  color: #fff;
  border: 1px solid var(--ribbon-jade-base);
  font-weight: 600;
  font-size: 14.5px;
  box-shadow: 0 4px 14px rgba(27, 94, 75, 0.3);
  cursor: pointer;
  transition: all var(--duration-fast) var(--ease-spring);
}

.letter-primary-btn:hover {
  background: var(--ribbon-jade-light);
  transform: translateY(-2px);
  box-shadow: 0 6px 20px rgba(27, 94, 75, 0.4);
}

.letter-primary-btn:active {
  transform: translateY(0) scale(0.98);
}

.letter-secondary-btn {
  padding: 10px 20px;
  border-radius: var(--radius-sm);
  background: #fff;
  color: var(--ink-secondary-wash);
  border: 1px solid var(--line-strong);
  font-size: 14px;
  font-weight: 550;
  cursor: pointer;
  box-shadow: var(--shadow-sm);
  transition: all var(--duration-fast) var(--ease-spring);
}

.letter-secondary-btn:hover {
  border-color: var(--wax-cinnabar-base);
  color: var(--wax-cinnabar-base);
  transform: translateY(-1.5px);
  box-shadow: var(--shadow);
}

/* ==========================================================================
   7. 动画序列 (Comprehensive Keyframes System)
   ========================================================================== */
@keyframes wax-crack-burst {
  0% { transform: translate(-50%, -50%) scale(1); opacity: 1; filter: blur(0); }
  40% { transform: translate(-50%, -50%) scale(1.18) rotate(6deg); opacity: 0.9; }
  100% { transform: translate(-50%, -50%) scale(1.6) rotate(18deg); opacity: 0; filter: blur(4px); }
}

@keyframes letter-glide-expand {
  0% { 
    opacity: 0; 
    top: 20px; 
    transform: translateX(-50%) translateY(40px) scale(0.88); 
  }
  50% { 
    opacity: 0.8; 
    transform: translateX(-50%) translateY(-50px) scale(1.02); 
  }
  100% { 
    opacity: 1; 
    top: -60px; 
    transform: translateX(-50%) translateY(-30px) scale(1); 
  }
}

@keyframes gold-fleck-shimmer {
  0% { opacity: 0.4; transform: scale(0.95); }
  50% { opacity: 0.8; transform: scale(1.05); }
  100% { opacity: 0.4; transform: scale(0.95); }
}

@keyframes ink-flow-reveal {
  from { opacity: 0; transform: translateY(6px); }
  to { opacity: 1; transform: translateY(0); }
}

/* ==========================================================================
   8. 响应式与打印适配 (Responsive & Print Media Queries)
   ========================================================================== */
@media (max-width: 768px) {
  .envelope-wrapper {
    width: 320px;
    height: 220px;
  }
  
  .wax-seal {
    width: 60px;
    height: 60px;
  }
  
  .wax-embossed-ring-outer {
    width: 44px;
    height: 44px;
  }
  
  .wax-embossed-ring-inner {
    width: 36px;
    height: 36px;
  }
  
  .wax-seal-emblem-text {
    font-size: 19px;
  }

  .letter-paper-body {
    padding: 32px 24px 28px;
  }

  .letter-salutation {
    font-size: 19px;
  }

  .letter-article {
    font-size: 14.5px;
    line-height: 1.85;
  }

  .welcome-letter-backdrop.is-opened .letter-paper-container {
    top: -10px;
    transform: translateX(-50%) translateY(0) scale(1);
    width: 96%;
    max-height: 88vh;
  }
  
  .letter-actions-bar {
    flex-direction: column;
    align-items: stretch;
    text-align: center;
  }
  
  .letter-buttons-group {
    justify-content: center;
  }
  
  .letter-signature-block {
    flex-direction: column;
    align-items: flex-end;
    gap: 12px;
  }
}

@media print {
  .welcome-letter-backdrop {
    position: static !important;
    background: #fff !important;
    padding: 0 !important;
    opacity: 1 !important;
    visibility: visible !important;
  }

  .envelope-wrapper,
  .welcome-close-trigger,
  .letter-actions-bar {
    display: none !important;
  }

  .letter-paper-container {
    position: static !important;
    transform: none !important;
    width: 100% !important;
    max-width: 100% !important;
    box-shadow: none !important;
    border: none !important;
  }

  .letter-paper-body {
    padding: 0 !important;
    border: none !important;
    background: #fff !important;
  }
  
  .letter-article {
    color: #000 !important;
    font-size: 12pt !important;
    line-height: 1.8 !important;
  }
}

/* ==========================================================================
   9. 深度微观物理质感与纸张折痕光影扩展 (Extended Physical Details)
   ========================================================================== */
.letter-paper-crease-top {
  position: absolute;
  top: 33.33%;
  left: 0;
  right: 0;
  height: 1px;
  background: linear-gradient(90deg, transparent 0%, var(--letter-paper-crease) 20%, var(--letter-paper-crease) 80%, transparent 100%);
  pointer-events: none;
}

.letter-paper-crease-bottom {
  position: absolute;
  top: 66.66%;
  left: 0;
  right: 0;
  height: 1px;
  background: linear-gradient(90deg, transparent 0%, var(--letter-paper-crease) 20%, var(--letter-paper-crease) 80%, transparent 100%);
  pointer-events: none;
}

.letter-ink-bleed-glow {
  text-shadow: 0 0 1px var(--ink-bleed-soft);
}

.letter-gold-flourish {
  color: var(--gold-emboss-base);
  display: inline-block;
  margin: 0 4px;
}

.wax-fragment-burst {
  position: absolute;
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--wax-cinnabar-bright);
  pointer-events: none;
  opacity: 0;
}

.welcome-letter-backdrop.is-opened .wax-fragment-burst {
  animation: wax-fragment-flight 0.6s var(--ease-spring) forwards;
}

@keyframes wax-fragment-flight {
  0% { transform: scale(1) translate(0, 0); opacity: 1; }
  100% { transform: scale(0) translate(var(--dx, 30px), var(--dy, -30px)); opacity: 0; }
}

.reopen-letter-floating-trigger {
  cursor: pointer;
  transition: all var(--duration-fast) var(--ease-spring);
}

.reopen-letter-floating-trigger:hover {
  transform: scale(1.05);
}

/* ==========================================================================
   10. 书法行气与宣纸纤维层级 (Calligraphic Rhythm & Xuan Paper Grain Layers)
   ========================================================================== */
.letter-paper-texture-layer {
  position: absolute;
  inset: 0;
  background: 
    radial-gradient(ellipse at top left, rgba(255, 255, 255, 0.4) 0%, transparent 50%),
    radial-gradient(ellipse at bottom right, rgba(160, 130, 95, 0.08) 0%, transparent 50%),
    linear-gradient(90deg, transparent 0%, rgba(184, 53, 34, 0.02) 50%, transparent 100%);
  pointer-events: none;
  border-radius: 10px;
}

.letter-ruled-column {
  position: relative;
  display: grid;
  gap: 16px;
}

.letter-ruled-column::before {
  content: "";
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  width: 1px;
  background: var(--letter-grid-faint);
}

/* 金石闲章：起首章与压角章 (Aesthetic Chinese Seals) */
.seal-opening-chapter {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 22px;
  height: 40px;
  border: 1.5px solid var(--wax-cinnabar-base);
  color: var(--wax-cinnabar-base);
  border-radius: 12px 12px 4px 4px;
  font: 700 11px/1.2 var(--serif);
  background: rgba(191, 45, 31, 0.04);
  box-shadow: 0 1px 3px rgba(191, 45, 31, 0.12);
  margin-right: 8px;
  vertical-align: middle;
  transform: rotate(-1deg);
}

.seal-corner-honor {
  position: absolute;
  bottom: 28px;
  left: 28px;
  width: 32px;
  height: 32px;
  border: 1.5px solid var(--wax-cinnabar-base);
  color: var(--wax-cinnabar-base);
  border-radius: 4px;
  font: 700 10px/1.1 var(--serif);
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  background: rgba(191, 45, 31, 0.04);
  transform: rotate(2deg);
  opacity: 0.85;
}

/* 诗意段落过渡首字微下沉 (Drop Cap Initial) */
.letter-initial-lead {
  float: left;
  font-size: 32px;
  line-height: 0.85;
  font-weight: 700;
  font-family: var(--serif);
  color: var(--wax-cinnabar-base);
  padding: 4px 8px 0 0;
}

/* 宣纸竖向折痕阴影梯度 (Vertical Crease Lighting) */
.letter-vertical-lighting {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 50%;
  width: 60px;
  transform: translateX(-50%);
  background: linear-gradient(90deg, transparent 0%, rgba(255, 255, 255, 0.18) 45%, rgba(120, 95, 70, 0.05) 55%, transparent 100%);
  pointer-events: none;
}

/* 底部温馨附言 (Postscript Box) */
.letter-postscript-box {
  margin-top: 24px;
  padding: 14px 20px;
  background: var(--letter-paper-warm);
  border: 1px solid var(--line-light);
  border-radius: var(--radius-sm);
  font-size: 13.5px;
  color: var(--ink-secondary-wash);
  line-height: 1.7;
}

.letter-postscript-title {
  font-weight: 650;
  color: var(--ribbon-jade-base);
  margin-right: 6px;
}

/* 重新阅读浮标触发器样式 (Reopen Trigger Badge in Settings & Home) */
.open-welcome-letter-badge {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 6px 14px;
  border-radius: var(--radius-full);
  background: var(--orange-soft);
  border: 1px solid var(--orange-border);
  color: var(--orange-dark);
  font-size: 13px;
  font-weight: 600;
  cursor: pointer;
  transition: all var(--duration-fast) var(--ease-spring);
}

.open-welcome-letter-badge:hover {
  background: var(--orange);
  color: #fff;
  transform: translateY(-1.5px);
  box-shadow: 0 4px 12px rgba(191, 45, 31, 0.25);
}

.open-welcome-letter-badge .badge-seal-char {
  width: 18px;
  height: 18px;
  border-radius: 50%;
  background: var(--wax-cinnabar-base);
  color: #fff;
  font: 700 10px/18px var(--serif);
  text-align: center;
}

/* ==========================================================================
   11. 高级微交互状态与焦点环 (Focus & Micro-Interactions)
   ========================================================================== */
.letter-dismiss-option:focus-within {
  outline: 2px solid var(--wax-cinnabar-bright);
  outline-offset: 2px;
  border-radius: 4px;
}

.letter-primary-btn:focus-visible,
.letter-secondary-btn:focus-visible {
  outline: 2px solid var(--ribbon-jade-base);
  outline-offset: 2px;
}

.letter-paper-container::-webkit-scrollbar {
  width: 6px;
}

.letter-paper-container::-webkit-scrollbar-track {
  background: transparent;
}

.letter-paper-container::-webkit-scrollbar-thumb {
  background: rgba(140, 110, 80, 0.3);
  border-radius: var(--radius-full);
}

.letter-paper-container::-webkit-scrollbar-thumb:hover {
  background: var(--ribbon-jade-base);
}

/* ==========================================================================
   12. 深度金石纹样与雅致笺纸底纹系统 (Detailed Paper Watermark Grid & Verses)
   ========================================================================== */
.letter-verse-block {
  margin: 18px 0;
  padding: 18px 24px;
  background: linear-gradient(135deg, rgba(251, 249, 244, 0.9) 0%, rgba(245, 241, 232, 0.7) 100%);
  border: 1px solid var(--letter-paper-edge);
  border-radius: var(--radius-sm);
  font-family: var(--serif);
  font-size: 15px;
  line-height: 1.9;
  color: var(--ink-primary-wash);
  text-align: center;
  position: relative;
  box-shadow: inset 0 1px 3px rgba(0, 0, 0, 0.02);
}

.letter-verse-block::before,
.letter-verse-block::after {
  content: "·";
  position: absolute;
  color: var(--wax-gold-leaf);
  font-size: 16px;
  opacity: 0.7;
}

.letter-verse-block::before {
  top: 8px;
  left: 12px;
}

.letter-verse-block::after {
  bottom: 8px;
  right: 12px;
}

.verse-line {
  margin: 4px 0;
  letter-spacing: 0.08em;
}

.verse-highlight {
  color: var(--wax-cinnabar-base);
  font-weight: 600;
}

/* 宣纸撕边边缘细微质感 (Deckled Edging Simulation) */
.deckled-edge-simulation {
  position: absolute;
  inset: 0;
  pointer-events: none;
  box-shadow: inset 0 0 12px rgba(180, 150, 120, 0.18);
  border-radius: 10px;
}

/* 金石闲章之印 (Authentic Minor Carved Stamps) */
.minor-seal-chrysanthemum {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 28px;
  height: 28px;
  border: 1.5px solid var(--ribbon-jade-base);
  color: var(--ribbon-jade-base);
  border-radius: 50%;
  font: 700 11px/1 var(--serif);
  background: rgba(27, 94, 75, 0.04);
  box-shadow: 0 1px 4px rgba(27, 94, 75, 0.12);
  margin-left: 6px;
}

.minor-seal-lotus {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 28px;
  height: 28px;
  border: 1.5px solid var(--wax-cinnabar-base);
  color: var(--wax-cinnabar-base);
  border-radius: 6px;
  font: 700 11px/1 var(--serif);
  background: rgba(191, 45, 31, 0.04);
  box-shadow: 0 1px 4px rgba(191, 45, 31, 0.12);
  margin-left: 6px;
}

/* 笺纸水墨浮雕题头 (Calligraphic Master Title) */
.letter-masthead-title {
  text-align: center;
  margin: 0 0 28px;
  position: relative;
}

.letter-masthead-title h2 {
  font: 600 clamp(24px, 2.8vw, 32px)/1.3 var(--serif);
  color: var(--ink-soot-black);
  margin: 0 0 6px;
  letter-spacing: 0.1em;
}

.letter-masthead-subtitle {
  font-size: 13px;
  color: var(--ink-faint-wash);
  font-family: var(--serif);
  letter-spacing: 0.16em;
  text-transform: uppercase;
}

/* 动效：展开后文字逐段微浮现 (Staggered Fade-in) */
.welcome-letter-backdrop.is-opened .letter-paragraph:nth-child(1) { animation: ink-flow-reveal 0.6s 0.2s backwards var(--ease-silk); }
.welcome-letter-backdrop.is-opened .letter-paragraph:nth-child(2) { animation: ink-flow-reveal 0.6s 0.3s backwards var(--ease-silk); }
.welcome-letter-backdrop.is-opened .letter-paragraph:nth-child(3) { animation: ink-flow-reveal 0.6s 0.4s backwards var(--ease-silk); }
.welcome-letter-backdrop.is-opened .letter-quote-callout { animation: ink-flow-reveal 0.6s 0.5s backwards var(--ease-silk); }
.welcome-letter-backdrop.is-opened .letter-paragraph:nth-child(5) { animation: ink-flow-reveal 0.6s 0.6s backwards var(--ease-silk); }
.welcome-letter-backdrop.is-opened .letter-verse-block { animation: ink-flow-reveal 0.6s 0.7s backwards var(--ease-silk); }
.welcome-letter-backdrop.is-opened .letter-paragraph:nth-child(7) { animation: ink-flow-reveal 0.6s 0.8s backwards var(--ease-silk); }
.welcome-letter-backdrop.is-opened .letter-signature-block { animation: ink-flow-reveal 0.6s 0.9s backwards var(--ease-silk); }

/* ==========================================================================
   13. 季节与心境主题定制色彩体系 (Seasonal Tone & Reading Nuances)
   ========================================================================== */
.welcome-letter-stage.theme-vernal-spring {
  --ribbon-jade-base: #1f6b55;
  --wax-cinnabar-base: #c23829;
}

.welcome-letter-stage.theme-autumn-harvest {
  --ribbon-jade-base: #7d500c;
  --wax-cinnabar-base: #a6361a;
  --letter-paper-base: #faf7ef;
}

.welcome-letter-stage.theme-winter-solstice {
  --ribbon-jade-base: #295270;
  --wax-cinnabar-base: #8f261b;
  --letter-paper-base: #f7f9fa;
}

/* ==========================================================================
   14. 光影折痕微观层叠规范 (Crease Shading Layer Hierarchy)
   ========================================================================== */
.crease-line-horizontal {
  position: absolute;
  left: 0;
  right: 0;
  height: 1px;
  background: linear-gradient(90deg, transparent 0%, var(--letter-paper-crease) 15%, var(--letter-paper-crease) 85%, transparent 100%);
  pointer-events: none;
}

.crease-line-horizontal.crease-1 { top: 25%; }
.crease-line-horizontal.crease-2 { top: 50%; }
.crease-line-horizontal.crease-3 { top: 75%; }

.crease-shadow-fold {
  position: absolute;
  left: 0;
  right: 0;
  height: 6px;
  background: linear-gradient(180deg, rgba(0, 0, 0, 0.03) 0%, transparent 100%);
  pointer-events: none;
}

.crease-shadow-fold.fold-1 { top: calc(25% + 1px); }
.crease-shadow-fold.fold-2 { top: calc(50% + 1px); }
.crease-shadow-fold.fold-3 { top: calc(75% + 1px); }

/* ==========================================================================
   15. 宣纸纤维水墨微噪点渲染 (Fiber & Ink Noise Filtration)
   ========================================================================== */
.xuan-fiber-noise-layer {
  position: absolute;
  inset: 0;
  opacity: 0.035;
  background-image: radial-gradient(#161c19 0.5px, transparent 0.5px);
  background-size: 8px 8px;
  pointer-events: none;
}

.letter-gold-powder-dust {
  position: absolute;
  inset: 0;
  opacity: 0.15;
  background: radial-gradient(circle at 70% 20%, rgba(212, 175, 55, 0.4) 0%, transparent 20%),
              radial-gradient(circle at 20% 80%, rgba(212, 175, 55, 0.3) 0%, transparent 25%);
  pointer-events: none;
}

/* ==========================================================================
   16. 高分辨率屏幕与视网膜显示适配 (Retina & High-DPI Display Polish)
   ========================================================================== */
@media (-webkit-min-device-pixel-ratio: 2), (min-resolution: 192dpi) {
  .letter-paper-body {
    border-width: 0.5px;
  }
  .wax-seal {
    box-shadow: 
      0 6px 20px var(--wax-shadow-depth),
      0 1px 4px var(--wax-shadow-glow),
      inset 0 1px 3px rgba(255, 255, 255, 0.5),
      inset 0 -2px 5px rgba(0, 0, 0, 0.6);
  }
  .envelope-box {
    box-shadow: 0 24px 60px var(--envelope-shadow-ambient), 0 4px 14px var(--envelope-shadow-drop);
  }
}

/* ==========================================================================
   17. 结束章标与书卷卷轴完备保障 (Final Seals & Scroll Integrity Assurances)
   ========================================================================== */
.letter-colophon-note {
  margin-top: 12px;
  font-size: 11.5px;
  color: var(--ink-faint-wash);
  text-align: right;
  letter-spacing: 0.06em;
  font-family: var(--serif);
}

.letter-colophon-note span {
  margin-left: 8px;
}