/* ============================================================
   Epistle — CSS 主样式
   结构：变量 → 主题 → 布局 → 组件 → 工具 → 响应式
   ============================================================ */

/* ── 变量：默认主题（白纸蓝墨） ── */
:root {
  --color-desk:    #E8E4DF;
  --color-paper:   #FFFFFF;
  --color-paper-rgb: 255, 255, 255;
  --color-ink:     #1C2333;
  --color-meta:    #718096;
  --color-accent:  #2C5282;
  --color-fold:    rgba(28, 35, 51, 0.08);
  --shadow-paper:  0 2px 20px rgba(0, 0, 0, 0.08);

  --font-body:     "Source Han Serif CN VF", "Noto Serif SC", "Source Han Serif SC", "Songti SC", "STSong", "SimSun", "宋体", serif;
  --font-title:     "QIJIFALLBACK", "Kaiti SC", "Kaiti TC", "STKaiti", "KaiTi", "楷体", serif;
  --font-signature: "LXGW WenKai Mono Screen", "Kaiti SC", "Kaiti TC", "STKaiti", "KaiTi", "楷体", serif;

  --width-content: 44rem;
  --width-sidebar: 14rem;
  --size-body:     18px;
  --line-height:   1.75;
  --spacing-para:  1.5rem;

  --dappled-enabled: 1;
  --paper-alpha: 0.9;
  --sun-scene-rotate: -18deg;
  --sun-blur-angle: 78deg;
  --sun-caster-blur: 7px;
  --sun-shadow-blend: multiply;
  --sun-ambient-primary: rgba(255, 246, 229, 0.88);
  --sun-ambient-secondary: rgba(255, 255, 255, 0.34);
  --sun-ambient-tertiary: rgba(255, 247, 235, 0.12);
  --sun-shadow-strong: rgba(82, 98, 117, 0.46);
  --sun-shadow-soft: rgba(126, 140, 156, 0.24);
  --sun-leaf-color: rgba(90, 104, 120, 0.34);
  --sun-paper-glow: rgba(255, 250, 241, 0.74);
  --sun-paper-glow-opacity: 0.72;
  --sun-bar-right: 24vw;
  --sun-bar-opacity: 0.34;
  --sun-grain-light: rgba(255, 255, 255, 0.08);
  --sun-grain-dark: rgba(41, 49, 58, 0.055);
  --sun-grain-opacity: 0.2;
  --paper-grain-opacity: 0.16;
}

/* ── 主题覆盖 ── */
[data-style="warm"] {
  --color-desk:    #D6C9B6;
  --color-paper:   #FEF9F0;
  --color-paper-rgb: 254, 249, 240;
  --color-ink:     #2C1F0E;
  --color-meta:    #8B7355;
  --color-accent:  #7B4F2E;
  --color-fold:    rgba(44, 31, 14, 0.08);

  --paper-alpha: 0.88;
  --sun-scene-rotate: -16deg;
  --sun-blur-angle: 74deg;
  --sun-caster-blur: 8px;
  --sun-ambient-primary: rgba(255, 223, 179, 0.9);
  --sun-ambient-secondary: rgba(255, 243, 221, 0.42);
  --sun-ambient-tertiary: rgba(255, 214, 160, 0.18);
  --sun-shadow-strong: rgba(123, 79, 36, 0.48);
  --sun-shadow-soft: rgba(169, 123, 76, 0.24);
  --sun-leaf-color: rgba(124, 83, 42, 0.36);
  --sun-paper-glow: rgba(255, 238, 206, 0.78);
  --sun-paper-glow-opacity: 0.8;
  --sun-bar-right: 21vw;
  --sun-bar-opacity: 0.38;
  --sun-grain-light: rgba(255, 246, 230, 0.1);
  --sun-grain-dark: rgba(94, 69, 43, 0.06);
  --sun-grain-opacity: 0.24;
  --paper-grain-opacity: 0.18;
}

[data-style="sky"] {
  --color-desk:    #C9DFF0;
  --color-paper:   #EBF4FB;
  --color-paper-rgb: 235, 244, 251;
  --color-ink:     #1A3A52;
  --color-meta:    #5A8FA8;
  --color-accent:  #1A6FA8;
  --color-fold:    rgba(26, 58, 82, 0.1);

  --paper-alpha: 0.9;
  --sun-scene-rotate: -21deg;
  --sun-blur-angle: 82deg;
  --sun-caster-blur: 6px;
  --sun-ambient-primary: rgba(223, 241, 255, 0.82);
  --sun-ambient-secondary: rgba(255, 255, 255, 0.32);
  --sun-ambient-tertiary: rgba(191, 226, 255, 0.14);
  --sun-shadow-strong: rgba(74, 122, 163, 0.34);
  --sun-shadow-soft: rgba(116, 156, 188, 0.18);
  --sun-leaf-color: rgba(82, 130, 170, 0.24);
  --sun-paper-glow: rgba(242, 250, 255, 0.7);
  --sun-paper-glow-opacity: 0.66;
  --sun-bar-right: 27vw;
  --sun-bar-opacity: 0.26;
  --sun-grain-light: rgba(255, 255, 255, 0.08);
  --sun-grain-dark: rgba(57, 103, 143, 0.05);
  --sun-grain-opacity: 0.17;
  --paper-grain-opacity: 0.14;
}

[data-style="night"] {
  --color-desk:    #0D1117;
  --color-paper:   #161B22;
  --color-paper-rgb: 22, 27, 34;
  --color-ink:     #CDD9E5;
  --color-meta:    #768390;
  --color-accent:  #79C0FF;
  --color-fold:    rgba(205, 217, 229, 0.1);
  --shadow-paper:  0 2px 20px rgba(0, 0, 0, 0.4);

  --paper-alpha: 0.86;
  --sun-scene-rotate: -12deg;
  --sun-blur-angle: 86deg;
  --sun-caster-blur: 10px;
  --sun-shadow-blend: soft-light;
  --sun-ambient-primary: rgba(68, 96, 141, 0.18);
  --sun-ambient-secondary: rgba(126, 174, 255, 0.08);
  --sun-ambient-tertiary: rgba(7, 12, 18, 0.16);
  --sun-shadow-strong: rgba(3, 8, 16, 0.72);
  --sun-shadow-soft: rgba(24, 36, 51, 0.36);
  --sun-leaf-color: rgba(8, 16, 27, 0.46);
  --sun-paper-glow: rgba(105, 146, 206, 0.18);
  --sun-paper-glow-opacity: 0.48;
  --sun-bar-right: 31vw;
  --sun-bar-opacity: 0.22;
  --sun-grain-light: rgba(255, 255, 255, 0.05);
  --sun-grain-dark: rgba(0, 0, 0, 0.14);
  --sun-grain-opacity: 0.24;
  --paper-grain-opacity: 0.18;
}

[data-style="spring"] {
  --color-desk:    #DDE8DC;
  --color-paper:   #F4FAF4;
  --color-paper-rgb: 244, 250, 244;
  --color-ink:     #1F3324;
  --color-meta:    #5A7A64;
  --color-accent:  #2D6A4F;
  --color-fold:    rgba(31, 51, 36, 0.08);

  --paper-alpha: 0.9;
  --sun-scene-rotate: -19deg;
  --sun-blur-angle: 76deg;
  --sun-caster-blur: 6px;
  --sun-ambient-primary: rgba(229, 244, 214, 0.88);
  --sun-ambient-secondary: rgba(244, 255, 239, 0.34);
  --sun-ambient-tertiary: rgba(198, 229, 181, 0.14);
  --sun-shadow-strong: rgba(78, 120, 88, 0.32);
  --sun-shadow-soft: rgba(112, 155, 118, 0.16);
  --sun-leaf-color: rgba(86, 134, 92, 0.26);
  --sun-paper-glow: rgba(245, 255, 240, 0.74);
  --sun-paper-glow-opacity: 0.74;
  --sun-bar-right: 24vw;
  --sun-bar-opacity: 0.24;
  --sun-grain-light: rgba(255, 255, 255, 0.08);
  --sun-grain-dark: rgba(58, 101, 67, 0.05);
  --sun-grain-opacity: 0.18;
  --paper-grain-opacity: 0.15;
}

[data-shadow-style="window"] {
  --sun-scene-rotate: -9deg;
  --sun-blur-angle: 66deg;
  --sun-caster-blur: 6px;
  --sun-bar-opacity: 0;
  --sun-paper-glow-opacity: 0.56;
}

[data-shadow-style="blinds"] {
  --sun-scene-rotate: -14deg;
  --sun-blur-angle: 72deg;
  --sun-caster-blur: 5px;
  --sun-bar-opacity: 0.1;
  --sun-paper-glow-opacity: 0.68;
}

[data-shadow-style="canopy"] {
  --sun-scene-rotate: -18deg;
}

/* ── 基础重置 ── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html { font-size: var(--size-body); scroll-behavior: smooth; }

body {
  font-family: var(--font-body);
  background-color: var(--color-desk);
  color: var(--color-ink);
  line-height: var(--line-height);
  min-height: 100vh;
  overflow-x: hidden;
}

body[data-dappled="off"] {
  --dappled-enabled: 0;
}

.sunlight-debug-chip {
  position: fixed;
  right: 0.85rem;
  bottom: 0.85rem;
  z-index: 1001;
  padding: 0.35rem 0.55rem;
  border-radius: 999px;
  font-size: 0.72rem;
  line-height: 1;
  letter-spacing: 0.04em;
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
  color: rgba(255, 255, 255, 0.92);
  background: rgba(16, 19, 24, 0.78);
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.18);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  pointer-events: none;
}

[data-style="night"] .sunlight-debug-chip {
  color: rgba(225, 235, 245, 0.92);
  background: rgba(8, 10, 14, 0.82);
}

/* ── 布局 ── */
.desk {
  position: relative;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

.sunlight-scene {
  position: fixed;
  inset: 0;
  overflow: hidden;
  pointer-events: none;
  z-index: 0;
}

.sunlight-scene[hidden] {
  display: none;
}

.sunlight-scene__ambient,
.sunlight-scene__projection,
.sunlight-scene__grain {
  position: absolute;
  inset: 0;
}

.sunlight-scene__ambient {
  inset: -16% -10% 12% -18%;
  opacity: calc(var(--dappled-enabled) * 0.96);
  background:
    radial-gradient(38rem 24rem at 84% 2%, var(--sun-ambient-primary) 0%, transparent 62%),
    radial-gradient(30rem 20rem at 62% 14%, var(--sun-ambient-secondary) 0%, transparent 60%),
    radial-gradient(28rem 18rem at 38% 18%, rgba(255, 255, 255, 0.16) 0%, transparent 62%),
    linear-gradient(180deg, var(--sun-ambient-tertiary) 0%, transparent 78%);
  filter: blur(34px);
  transform: rotate(var(--sun-scene-rotate));
  transform-origin: top right;
}

.sunlight-scene__projection {
  inset: -14vh -24vw -10vh -28vw;
  transform: rotate(var(--sun-scene-rotate));
  transform-origin: top right;
  perspective: 120vw;
}

.sunlight-scene__shutters,
.sunlight-scene__branches,
.sunlight-scene__leaves {
  position: absolute;
  inset: 0;
}

.sunlight-shutter {
  position: absolute;
  mix-blend-mode: var(--sun-shadow-blend);
}

.sunlight-shutter--canopy-band {
  border-top: 10px solid transparent;
  border-bottom: 10px solid transparent;
  clip-path: polygon(0 0, 100% 0, 88% 100%, 0 100%);
  background: linear-gradient(90deg, var(--sun-shadow-strong) 0 28%, var(--sun-shadow-soft) 56%, transparent 86%);
  filter: blur(var(--sun-caster-blur));
  transform: translateX(var(--sunlight-shift)) rotateY(var(--sunlight-tilt)) skewX(var(--sunlight-skew));
  transform-origin: right center;
}

.sunlight-shutter--blind {
  border-radius: 999px;
  background: linear-gradient(90deg, var(--sun-shadow-strong) 0%, var(--sun-shadow-soft) 58%, transparent 100%);
  filter: blur(calc(var(--sun-caster-blur) * 1.05));
  transform: translateX(var(--sunlight-shift)) rotate(var(--sunlight-tilt));
  transform-origin: right center;
}

.sunlight-shutter--blind-rail {
  border-radius: 999px;
  background: linear-gradient(180deg, var(--sun-shadow-strong) 0%, var(--sun-shadow-soft) 68%, transparent 100%);
  filter: blur(8px);
}

.sunlight-shutter--window-v,
.sunlight-shutter--window-h,
.sunlight-shutter--window-sash {
  border-radius: 999px;
  background: linear-gradient(90deg, var(--sun-shadow-strong) 0%, var(--sun-shadow-soft) 68%, transparent 100%);
  filter: blur(calc(var(--sun-caster-blur) * 1.1));
}

.sunlight-shutter--window-v {
  transform: rotate(var(--sunlight-tilt));
  transform-origin: center top;
}

.sunlight-shutter--window-h {
  transform: rotate(-1.5deg);
  transform-origin: left center;
}

.sunlight-shutter--window-sash {
  filter: blur(6px);
}

.sunlight-branch {
  position: absolute;
  border-radius: 999px;
  background: linear-gradient(90deg, var(--sun-shadow-strong) 0%, var(--sun-shadow-soft) 72%, transparent 100%);
  filter: blur(2px);
  transform-origin: left center;
  mix-blend-mode: var(--sun-shadow-blend);
}

.sunlight-branch--primary {
  filter: blur(2.4px);
}

.sunlight-branch--twig {
  filter: blur(1.8px);
}

.sunlight-scene__bar {
  position: absolute;
  top: -12vh;
  right: var(--sun-bar-right);
  width: 26px;
  height: 130vh;
  border-radius: 999px;
  background: linear-gradient(180deg, var(--sun-shadow-strong) 0%, var(--sun-shadow-soft) 65%, transparent 100%);
  filter: blur(8px);
  opacity: calc(var(--dappled-enabled) * var(--sun-bar-opacity));
  mix-blend-mode: var(--sun-shadow-blend);
}

.sunlight-leaf {
  position: absolute;
  width: calc(var(--leaf-size) * 0.74);
  height: var(--leaf-size);
  opacity: var(--leaf-opacity);
  filter: blur(var(--leaf-blur));
  transform: rotate(var(--leaf-rotation)) scale(var(--leaf-scale));
  transform-origin: center;
  mix-blend-mode: var(--sun-shadow-blend);
}

.sunlight-leaf::before,
.sunlight-leaf::after {
  content: "";
  position: absolute;
  background: var(--sun-leaf-color);
}

.sunlight-leaf--1::before {
  inset: 0;
  clip-path: polygon(50% 0%, 63% 8%, 77% 18%, 73% 31%, 92% 36%, 82% 50%, 100% 60%, 78% 70%, 84% 85%, 62% 79%, 50% 100%, 38% 79%, 16% 85%, 22% 70%, 0% 60%, 18% 50%, 8% 36%, 27% 31%, 23% 18%, 37% 8%);
}

.sunlight-leaf--2::before {
  inset: 2% 10% 0 0;
  clip-path: polygon(50% 0%, 69% 9%, 86% 25%, 77% 40%, 95% 54%, 76% 69%, 80% 86%, 57% 81%, 49% 100%, 37% 80%, 15% 86%, 22% 68%, 0% 55%, 20% 40%, 11% 25%, 31% 10%);
  transform: rotate(-10deg);
}

.sunlight-leaf--2::after {
  inset: 24% -6% 8% 38%;
  clip-path: polygon(47% 0%, 66% 14%, 84% 34%, 100% 52%, 79% 74%, 55% 100%, 33% 76%, 12% 55%, 24% 32%);
  transform: rotate(14deg);
}

.sunlight-leaf--3::before {
  inset: 3% 18% 0 0;
  clip-path: polygon(48% 0%, 64% 10%, 82% 28%, 73% 42%, 92% 56%, 70% 73%, 74% 88%, 54% 82%, 47% 100%, 32% 81%, 12% 88%, 18% 71%, 0% 56%, 22% 42%, 13% 27%, 31% 10%);
  transform: rotate(-14deg);
}

.sunlight-leaf--3::after {
  inset: 16% 0 8% 22%;
  clip-path: polygon(52% 0%, 68% 11%, 86% 30%, 77% 44%, 100% 58%, 78% 76%, 81% 92%, 56% 84%, 48% 100%, 34% 84%, 12% 92%, 21% 75%, 0% 58%, 21% 44%, 13% 29%, 31% 11%);
  transform: rotate(11deg);
}

.sunlight-leaf--4::before {
  inset: 0 12% 4% 12%;
  clip-path: polygon(50% 0%, 63% 13%, 82% 16%, 76% 32%, 98% 40%, 83% 54%, 95% 72%, 72% 72%, 67% 92%, 50% 82%, 33% 92%, 28% 72%, 5% 72%, 17% 54%, 2% 40%, 24% 32%, 18% 16%, 37% 13%);
}

.sunlight-leaf--4::after {
  inset: 36% -10% 18% 36%;
  clip-path: polygon(46% 0%, 66% 16%, 84% 36%, 100% 54%, 80% 76%, 56% 100%, 34% 78%, 12% 55%, 22% 32%);
  transform: rotate(18deg);
}

.sunlight-leaf--canopy {
  filter: blur(calc(var(--leaf-blur) * 0.82));
}

.sunlight-leaf--drift {
  animation: sunlightLeafDrift var(--leaf-duration, 24s) ease-in-out var(--leaf-delay, 0s) infinite alternate;
}

.sunlight-scene__grain {
  background-image:
    radial-gradient(var(--sun-grain-light) 0.55px, transparent 0.8px),
    radial-gradient(var(--sun-grain-dark) 0.55px, transparent 0.8px);
  background-position: 0 0, 9px 12px;
  background-size: 18px 18px, 23px 23px;
}

.sunlight-scene__grain {
  opacity: calc(var(--dappled-enabled) * var(--sun-grain-opacity));
  mix-blend-mode: soft-light;
  animation: sunlightNoise 1.8s steps(2) infinite;
}

.layout,
.site-header,
.site-footer {
  position: relative;
  z-index: 1;
}

.layout {
  display: flex;
  flex: 1;
  max-width: calc(var(--width-content) + 4rem);
  margin: 0 auto;
  width: 100%;
  padding: 0 1.5rem;
}

/* ── 信纸（主内容） ── */
.paper {
  position: relative;
  isolation: isolate;
  overflow: hidden;
  background: linear-gradient(
    180deg,
    rgba(var(--color-paper-rgb), calc(var(--paper-alpha) + 0.05)) 0%,
    rgba(var(--color-paper-rgb), var(--paper-alpha)) 38%,
    rgba(var(--color-paper-rgb), calc(var(--paper-alpha) - 0.04)) 100%
  );
  box-shadow: var(--shadow-paper);
  padding: 3rem 3.5rem 4rem;
  border-right: 1px solid var(--color-fold);
  min-height: calc(100vh - 8rem);
  backdrop-filter: blur(14px) saturate(118%) brightness(1.02);
  -webkit-backdrop-filter: blur(14px) saturate(118%) brightness(1.02);
}

.paper > * {
  position: relative;
  z-index: 1;
}

body[data-dappled="off"] .sunlight-scene {
  display: none;
}

@supports not ((backdrop-filter: blur(1px)) or (-webkit-backdrop-filter: blur(1px))) {
  .paper {
    background: linear-gradient(
      180deg,
      rgba(var(--color-paper-rgb), 0.92) 0%,
      rgba(var(--color-paper-rgb), 0.9) 100%
    );
  }
}

/* ── 页眉 ── */
.site-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 1.25rem 1.5rem;
  max-width: calc(var(--width-content) + var(--width-sidebar) + 4rem);
  margin: 0 auto;
  width: 100%;
}

.site-title {
  font-size: 1rem;
  font-weight: 600;
  color: var(--color-ink);
  text-decoration: none;
  letter-spacing: 0.05em;
}

/* ── 信笺索引标签 ── */
.index-tab {
  position: fixed;
  right: -2px;
  top: 5rem;
  z-index: 200;

  /* 牛皮纸标签页 */
  background: rgba(var(--color-paper-rgb), 0.7);
  color: var(--color-meta);
  border: 1px solid var(--color-fold);
  border-right: none;
  border-radius: 4px 0 0 4px;
  padding: 0.8rem 0.35rem;

  /* 竖排文字 */
  writing-mode: vertical-rl;
  font-family: var(--font-body);
  font-size: 0.75rem;
  font-weight: 400;
  letter-spacing: 0.25em;

  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
  -webkit-appearance: none;
  appearance: none;
  box-shadow: -1px 1px 4px rgba(0, 0, 0, 0.06);
  transition: all 0.3s ease;
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
}

.index-tab:focus,
.index-tab:focus-visible { outline: none; }

.index-tab:hover {
  background: rgba(var(--color-paper-rgb), 0.88);
  padding-right: 0.5rem;
  box-shadow: -2px 2px 8px rgba(0, 0, 0, 0.1);
  color: var(--color-ink);
}

.index-tab.is-active {
  background: rgba(var(--color-paper-rgb), 0.92);
  color: var(--color-ink);
  /* 跟随侧边栏移动到其内部 */
  right: min(320px, 85vw);
}

/* ── 信件正文结构 ── */
.letter { max-width: var(--width-content); }

.letter-header {
  margin-bottom: 1.5rem;
  text-align: center;
}

.letter .letter-title {
  font-family: var(--font-title);
  font-size: 2rem;
  font-weight: 400;
  line-height: 1.4;
}

.letter-body h1,
.letter-body h2,
.letter-body h3,
.letter-body h4,
.letter-body h5,
.letter-body h6 {
  font-family: "Kaiti SC", "Kaiti TC", "STKaiti", "KaiTi", "楷体", "AR PL UKai CN", serif;
  font-weight: 400;
}

.letter-date {
  font-size: 0.85rem;
  color: var(--color-meta);
  display: block;
}

.letter-date--footer {
  display: block;
  margin-top: 1rem;
  font-size: 0.875rem;
}

.letter-body p + p { margin-top: var(--spacing-para); }

/* ── 继续展信链接 ── */
.read-more {
  display: inline-block;
  margin-top: 2rem;
  color: var(--color-accent);
  text-decoration: none;
  font-size: 0.9rem;
  border-bottom: 1px solid currentColor;
  padding-bottom: 1px;
  transition: opacity 0.2s;
}

.read-more:hover { opacity: 0.7; }

/* ── 文章末尾（署名区） ── */
.letter-footer {
  margin-top: 3rem;
  padding-top: 2rem;
  text-align: right;
}

.valediction {
  color: var(--color-meta);
  margin-bottom: 0.5rem;
}

.signature {
  margin-top: 1rem;
}

.signature-text {
  font-family: var(--font-signature);
  font-size: 1.75rem;
  color: var(--color-ink);
}

.signature-image {
  max-height: 3rem;
  display: inline-block;
}

.postscript {
  margin-top: 1.5rem;
  font-size: 0.9rem;
  color: var(--color-meta);
}

/* ── 信件导航 ── */
.letter-nav {
  margin-top: 3rem;
  padding-top: 2rem;
  border-top: 1px solid var(--color-fold);
  display: flex;
  justify-content: space-between;
  gap: 1rem;
}

.letter-nav__link {
  display: flex;
  flex-direction: column;
  text-decoration: none;
  color: var(--color-ink);
  max-width: 45%;
  transition: color 0.2s;
}

.letter-nav__link:hover {
  color: var(--color-accent);
}

.letter-nav__link--next {
  align-items: flex-start;
}

.letter-nav__link--prev {
  align-items: flex-end;
  text-align: right;
  margin-left: auto;
}

.letter-nav__label {
  font-size: 0.75rem;
  color: var(--color-meta);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 0.25rem;
}

.letter-nav__title {
  font-size: 0.95rem;
  line-height: 1.4;
}

@keyframes sunlightLeafDrift {
  0% {
    transform: translate3d(0, 0, 0) rotate(var(--leaf-rotation)) scale(var(--leaf-scale));
  }
  100% {
    transform: translate3d(-1rem, 0.75rem, 0) rotate(calc(var(--leaf-rotation) + 9deg)) scale(calc(var(--leaf-scale) * 1.04));
  }
}

@keyframes sunlightNoise {
  0% { transform: translate3d(0, 1rem, 0); }
  20% { transform: translate3d(-0.75rem, -0.75rem, 0); }
  40% { transform: translate3d(0.5rem, 1.25rem, 0); }
  60% { transform: translate3d(-1rem, 0.25rem, 0); }
  80% { transform: translate3d(0.75rem, -1rem, 0); }
  100% { transform: translate3d(-0.5rem, 0, 0); }
}

/* ── 侧边栏（归档） ── */
.sidebar {
  position: fixed;
  top: 0;
  right: 0;
  bottom: 0;
  width: min(320px, 85vw);
  padding: 3rem 1.25rem 2rem 1.5rem;
  background: #FDFBF7;
  z-index: 100;
  overflow-y: auto;
  box-shadow: -4px 0 20px rgba(0, 0, 0, 0.12);
  
  /* 默认隐藏，从右侧滑入 */
  transform: translateX(100%);
  transition: transform 0.35s ease;
}

.sidebar.is-open {
  transform: translateX(0);
}

.archive-title {
  font-size: 0.75rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--color-meta);
  margin-bottom: 1.25rem;
}

.year-toggle {
  background: none;
  border: none;
  cursor: pointer;
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--color-meta);
  letter-spacing: 0.05em;
  padding: 0;
  margin-bottom: 0.5rem;
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

.year-toggle::before {
  content: "▸";
  font-size: 0.6rem;
  transition: transform 0.2s;
}

.year-toggle[aria-expanded="true"]::before { transform: rotate(90deg); }

.month-list { margin-bottom: 1rem; }

.month-group {
  display: grid;
  grid-template-columns: 2rem 1fr;
  gap: 0 0.5rem;
  margin-bottom: 0.25rem;
}

.month-label {
  font-size: 0.7rem;
  color: var(--color-meta);
  padding-top: 0.15rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.month-group ul { list-style: none; }

.month-group a {
  display: flex;
  gap: 0.5rem;
  font-size: 0.8rem;
  color: var(--color-ink);
  text-decoration: none;
  padding: 0.15rem 0;
  line-height: 1.4;
  transition: color 0.15s;
}

.month-group a:hover { color: var(--color-accent); }
.month-group a[aria-current="page"] { color: var(--color-accent); font-weight: 600; }

.month-group time {
  flex-shrink: 0;
  color: var(--color-meta);
  font-size: 0.75rem;
}

/* ── 链接（正文内） ── */
.letter-body a {
  color: var(--color-accent);
  text-decoration: underline;
  text-underline-offset: 3px;
  text-decoration-thickness: 1px;
  transition: text-underline-offset 0.2s, opacity 0.2s;
}

.letter-body a:hover {
  text-underline-offset: 5px;
  opacity: 0.75;
}

/* ── 称谓 ── */
.salutation {
  font-style: italic;
  color: var(--color-meta);
  margin-bottom: 1.5rem;
}

/* ── 移动端侧边栏遮罩 ── */
.sidebar-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.35);
  z-index: 99;
}

.sidebar-overlay.is-visible { display: block; }

/* ── 页脚 ── */
.site-footer {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 1rem 1.5rem;
  font-size: 0.8rem;
  color: var(--color-meta);
  max-width: calc(var(--width-content) + var(--width-sidebar) + 4rem);
  margin: 0 auto;
  width: 100%;
}

.back-to-top {
  color: var(--color-meta);
  text-decoration: none;
  font-size: 1rem;
}

.back-to-top:hover { color: var(--color-accent); }

/* ── Heti 覆盖（字体栈） ── */
.heti.heti--serif {
  font-family: var(--font-body);
}

/* ── 响应式：移动端 ── */
@media (max-width: 768px) {
  :root { --size-body: 16px; }

  .sunlight-scene__ambient {
    inset: -12% -18% 32% -20%;
    opacity: calc(var(--dappled-enabled) * 0.74);
  }

  .sunlight-scene__projection {
    inset: -10vh -28vw -12vh -30vw;
  }

  .sunlight-scene__bar {
    width: 18px;
    right: 18vw;
  }

  .sunlight-scene__grain {
    opacity: calc(var(--dappled-enabled) * 0.12);
  }

  .layout {
    padding: 0;
  }

  .paper {
    padding: 1.5rem 1.25rem 3rem;
    border-right: none;
    box-shadow: none;
    backdrop-filter: blur(10px) saturate(110%) brightness(1.02);
    -webkit-backdrop-filter: blur(10px) saturate(110%) brightness(1.02);
  }

  .sidebar {
    width: min(280px, 80vw);
  }

  .site-header { padding: 1rem 1.25rem; }

  /* 移动端标签调整 */
  .index-tab {
    padding: 0.6rem 0.3rem;
    font-size: 0.7rem;
    top: 4rem;
  }

  .index-tab.is-active {
    right: min(280px, 80vw);
  }

  .sidebar {
    width: min(280px, 80vw);
  }
}

@media (prefers-reduced-motion: reduce) {
  .sunlight-scene__grain,
  .sunlight-leaf--drift {
    animation: none;
  }

  .sunlight-scene__ambient {
    opacity: calc(var(--dappled-enabled) * 0.8);
  }
}

/* ============================================================
   Heti 深度集成
   ============================================================ */

/* ── night 模式桥接（Heti 用 prefers-color-scheme: dark，
       我们用 data-style="night"，需手动补齐） ── */
[data-style="night"] .heti blockquote {
  background-color: rgba(255, 255, 255, 0.06);
}
[data-style="night"] .heti hr {
  background-color: #404040;
}
[data-style="night"] .heti pre,
[data-style="night"] .heti code:not(pre > code) {
  background-color: rgba(255, 255, 255, 0.06);
  color: inherit;
}
[data-style="night"] .heti mark {
  background-color: rgba(255, 220, 0, 0.2);
  color: inherit;
}
[data-style="night"] .heti table thead {
  background-color: rgba(255, 255, 255, 0.06);
}
[data-style="night"] .heti a {
  color: var(--color-accent);
}

/* ── 让所有主题的 Heti 颜色继承我们的 CSS 变量 ── */
.heti {
  color: var(--color-ink);
}
.heti .heti-meta,
.heti-meta {
  color: var(--color-meta);
  font-size: 0.8em;
  font-style: normal;
  letter-spacing: 0.02em;
}
.heti a {
  color: var(--color-accent);
}

/* ── 诗词落款居中 ── */
.verse-byline {
  text-align: center;
  margin-top: -0.75rem;
  margin-bottom: 1.25rem;
}

/* ── Heti 字号类的显式定义（确保跨主题可见） ── */
.heti-x-large { font-size: 1.4em; }
.heti-large   { font-size: 1.15em; }
.heti-small   { font-size: 0.85em; }
.heti-x-small { font-size: 0.7em; }

/* ── 诗词版式：居中对齐 ── */
.heti--poetry {
  text-align: center;
}
.heti--poetry h2 {
  margin-bottom: 1.5rem;
}

/* ── 古文版式：缩进调整 ── */
.heti--ancient p {
  text-indent: 2em;
}

/* ── 竖排：容器高度限制 ── */
.heti--vertical {
  max-height: 42em;
  overflow-x: auto;
}

/* ── 多栏：栏间距 ── */
[class*="heti--columns-"] {
  column-gap: 2em;
  column-rule: 1px solid var(--color-fold);
}

/* ── shortcode 块与信件正文的间距 ── */
.letter-body .heti--poetry,
.letter-body .heti--ancient,
.letter-body .heti--vertical,
[class*="letter-body .heti--columns"] {
  margin-block: 2rem;
  padding: 1.5rem 2rem;
  border: 1px solid var(--color-fold);
  border-radius: 2px;
}

/* ============================================================
   Unified Dappled Layer — CSS-Tricks effect + theme-switch architecture
   ============================================================ */
:root {
  --dappled-paper-alpha: 0.72;
  --dappled-shadow-color: rgba(40, 50, 65, 0.62);
  --dappled-shadow-blur: 20px;
  --dappled-shadow-opacity: 1;
  --dappled-light-color: rgba(255, 255, 255, 0.6);
  --dappled-bokeh-color: rgba(255, 248, 230, 0.85);
  --dappled-bokeh-blur: 18px;
  --dappled-bokeh-opacity: 0.9;
  --dappled-wash-1: rgba(255, 246, 231, 0.84);
  --dappled-wash-2: rgba(255, 255, 255, 0.26);
  --dappled-grain-opacity: 0.12;
}

[data-style="warm"] {
  --dappled-paper-alpha: 0.70;
  --dappled-shadow-color: rgba(75, 45, 15, 0.64);
  --dappled-shadow-blur: 18px;
  --dappled-light-color: rgba(255, 245, 220, 0.65);
  --dappled-bokeh-color: rgba(255, 238, 200, 0.88);
  --dappled-bokeh-blur: 16px;
  --dappled-bokeh-opacity: 0.92;
  --dappled-wash-1: rgba(255, 225, 184, 0.88);
  --dappled-wash-2: rgba(255, 244, 222, 0.28);
  --dappled-grain-opacity: 0.14;
}

[data-style="sky"] {
  --dappled-paper-alpha: 0.72;
  --dappled-shadow-color: rgba(34, 66, 98, 0.54);
  --dappled-shadow-blur: 16px;
  --dappled-light-color: rgba(255, 255, 255, 0.7);
  --dappled-bokeh-color: rgba(240, 250, 255, 0.82);
  --dappled-bokeh-blur: 14px;
  --dappled-bokeh-opacity: 0.92;
  --dappled-wash-1: rgba(221, 241, 255, 0.82);
  --dappled-wash-2: rgba(255, 255, 255, 0.24);
  --dappled-grain-opacity: 0.11;
}

[data-style="night"] {
  --dappled-paper-alpha: 0.86;
  --dappled-shadow-color: rgba(0, 4, 14, 0.48);
  --dappled-shadow-blur: 22px;
  --dappled-shadow-opacity: 0.7;
  --dappled-light-color: rgba(200, 215, 240, 0.3);
  --dappled-bokeh-color: rgba(180, 200, 240, 0.35);
  --dappled-bokeh-blur: 22px;
  --dappled-bokeh-opacity: 0.65;
  --dappled-wash-1: rgba(74, 102, 148, 0.2);
  --dappled-wash-2: rgba(124, 170, 255, 0.06);
  --dappled-grain-opacity: 0.16;
}

[data-style="spring"] {
  --dappled-paper-alpha: 0.70;
  --dappled-shadow-color: rgba(32, 62, 36, 0.56);
  --dappled-shadow-blur: 16px;
  --dappled-light-color: rgba(255, 252, 235, 0.55);
  --dappled-bokeh-color: rgba(255, 245, 210, 0.82);
  --dappled-bokeh-blur: 16px;
  --dappled-bokeh-opacity: 0.88;
  --dappled-wash-1: rgba(228, 244, 214, 0.84);
  --dappled-wash-2: rgba(244, 255, 239, 0.24);
  --dappled-grain-opacity: 0.11;
}

body[data-dappled="off"] {
  --dappled-paper-alpha: 0.96;
}

.dappled-layer {
  position: fixed;
  inset: 0;
  overflow: hidden;
  pointer-events: none;
  z-index: 0;
}

body[data-dappled="off"] .dappled-layer {
  display: none;
}

.dappled-layer__wash,
.dappled-layer__shapes,
.dappled-layer__grain {
  position: absolute;
  inset: 0;
}

.dappled-layer__wash {
  inset: -12% -12% -6% -14%;
  opacity: calc(var(--dappled-enabled) * 0.96);
  background:
    radial-gradient(42rem 28rem at 82% 4%, var(--dappled-wash-1) 0%, transparent 56%),
    radial-gradient(30rem 24rem at 58% 18%, var(--dappled-wash-2) 0%, transparent 58%),
    linear-gradient(180deg, rgba(255, 255, 255, 0.08) 0%, transparent 72%);
  filter: blur(38px);
}

.dappled-layer__shadows {
  position: absolute;
  inset: -8%;
  filter: blur(var(--dappled-shadow-blur, 4px));
  opacity: calc(var(--dappled-enabled) * var(--dappled-shadow-opacity, 1));
  animation: dappledDrift 36s ease-in-out infinite alternate;
}

.dappled-layer__bokeh {
  position: absolute;
  inset: -8%;
  filter: blur(var(--dappled-bokeh-blur, 18px));
  opacity: calc(var(--dappled-enabled) * var(--dappled-bokeh-opacity, 0.7));
  animation: dappledDrift 30s ease-in-out -8s infinite alternate;
}

/* Leaf/canopy shadow fragments — elliptical, directional */
.dappled-shadow {
  position: absolute;
  border-radius: 50%;
  background: radial-gradient(
    ellipse,
    var(--dappled-shadow-color) 0%,
    transparent 68%
  );
}

/* Large shadow mass — tree canopy blocking area, soft edges */
.dappled-mass {
  position: absolute;
  border-radius: 42% 58% 55% 45% / 48% 40% 60% 52%;
  background: radial-gradient(
    ellipse,
    var(--dappled-shadow-color) 0%,
    rgba(0,0,0,0.02) 65%,
    transparent 85%
  );
}

/* Branch shadows — long, thin, angled */
.dappled-branch {
  position: absolute;
  border-radius: 40%;
  background: linear-gradient(
    90deg,
    var(--dappled-shadow-color) 0%,
    transparent 100%
  );
  transform-origin: left center;
}

/* Blinds light stripes — repeating diagonal light bands cutting through shadow */
.dappled-blinds {
  position: absolute;
  inset: -20%;
  background: repeating-linear-gradient(
    var(--blinds-angle, -35deg),
    transparent 0px,
    transparent var(--blinds-gap, 18px),
    var(--dappled-shadow-color) var(--blinds-gap, 18px),
    var(--dappled-shadow-color) calc(var(--blinds-gap, 18px) + var(--blinds-width, 10px))
  );
}

/* Window bar — thin structural shadow (vertical or horizontal) */
.dappled-bar {
  position: absolute;
  background: linear-gradient(
    var(--bar-dir, 180deg),
    transparent 0%,
    var(--dappled-shadow-color) 15%,
    var(--dappled-shadow-color) 85%,
    transparent 100%
  );
}

/* Diamond shadow grid — dark rounded diamonds, bright gaps = light through window */
.dappled-diamond {
  position: absolute;
  background: var(--dappled-shadow-color);
  border-radius: 22%;
  transform: rotate(45deg);
}

/* Warm bokeh light spots */
.dappled-bokeh {
  position: absolute;
  border-radius: 50%;
  background: radial-gradient(
    circle,
    var(--dappled-bokeh-color) 0%,
    transparent 72%
  );
}

/* Light rays — bright streaks from window/canopy (screen blend) */
.dappled-light {
  position: absolute;
  background: linear-gradient(
    var(--light-dir, 90deg),
    transparent 0%,
    var(--dappled-light-color) 18%,
    var(--dappled-light-color) 82%,
    transparent 100%
  );
}

.dappled-layer__grain {
  background-image:
    radial-gradient(rgba(255, 255, 255, 0.08) 0.55px, transparent 0.8px),
    radial-gradient(rgba(31, 39, 49, 0.05) 0.55px, transparent 0.8px);
  background-position: 0 0, 9px 12px;
  background-size: 18px 18px, 23px 23px;
  opacity: calc(var(--dappled-enabled) * var(--dappled-grain-opacity));
  mix-blend-mode: soft-light;
  animation: dappledNoise 2.2s steps(2) infinite;
}

.layout,
.site-header,
.site-footer {
  position: relative;
  z-index: 1;
}

.paper {
  position: relative;
  isolation: isolate;
  overflow: hidden;
  background: linear-gradient(
    180deg,
    rgba(var(--color-paper-rgb), calc(var(--dappled-paper-alpha) + 0.05)) 0%,
    rgba(var(--color-paper-rgb), var(--dappled-paper-alpha)) 38%,
    rgba(var(--color-paper-rgb), calc(var(--dappled-paper-alpha) - 0.04)) 100%
  );
  backdrop-filter: blur(14px) saturate(118%) brightness(1.02);
  -webkit-backdrop-filter: blur(14px) saturate(118%) brightness(1.02);
}

.paper::before {
  content: "";
  position: absolute;
  inset: 0;
  pointer-events: none;
  z-index: 0;
  background: linear-gradient(180deg, rgba(255, 255, 255, 0.16) 0%, transparent 28%, rgba(255, 255, 255, 0.08) 100%);
}

.paper > * {
  position: relative;
  z-index: 1;
}

@supports not ((backdrop-filter: blur(1px)) or (-webkit-backdrop-filter: blur(1px))) {
  .paper {
    background: linear-gradient(
      180deg,
      rgba(var(--color-paper-rgb), 0.92) 0%,
      rgba(var(--color-paper-rgb), 0.9) 100%
    );
  }
}

@keyframes dappledDrift {
  0% { transform: translate3d(0, 0, 0) scale(1); }
  100% { transform: translate3d(-1.8rem, 1.2rem, 0) scale(1.02); }
}

@keyframes dappledNoise {
  0% { transform: translate3d(0, 1rem, 0); }
  20% { transform: translate3d(-0.75rem, -0.75rem, 0); }
  40% { transform: translate3d(0.5rem, 1.25rem, 0); }
  60% { transform: translate3d(-1rem, 0.25rem, 0); }
  80% { transform: translate3d(0.75rem, -1rem, 0); }
  100% { transform: translate3d(-0.5rem, 0, 0); }
}

@media (max-width: 768px) {
  .dappled-layer__wash {
    inset: -12% -18% -2% -22%;
  }

  .dappled-layer__shadows {
    --dappled-shadow-blur: 14px;
    --dappled-shadow-opacity: 0.8;
  }

  .dappled-layer__bokeh {
    --dappled-bokeh-blur: 20px;
    --dappled-bokeh-opacity: 0.5;
  }

  .dappled-layer__grain {
    opacity: calc(var(--dappled-enabled) * 0.09);
  }

  .paper {
    backdrop-filter: blur(10px) saturate(110%) brightness(1.02);
    -webkit-backdrop-filter: blur(10px) saturate(110%) brightness(1.02);
  }
}

@media (prefers-reduced-motion: reduce) {
  .dappled-layer__shadows,
  .dappled-layer__bokeh,
  .dappled-layer__grain {
    animation: none;
  }
}