/* ============================================================
   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-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:     "Inter", -apple-system, "Helvetica Neue", system-ui,
                   "Source Han Serif SC", "Noto Serif SC", "Songti SC", "Songti TC", "STSong", "SimSun", serif;
  --font-signature: "Caveat", "Dancing Script", cursive;

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

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

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

[data-style="night"] {
  --color-desk:    #0D1117;
  --color-paper:   #161B22;
  --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);
}

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

/* ── 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;
}

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

.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 {
  background: var(--color-paper);
  box-shadow: var(--shadow-paper);
  padding: 3rem 3.5rem 4rem;
  border-right: 1px solid var(--color-fold);
  min-height: calc(100vh - 8rem);
}

/* ── 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: 0;
  top: 5rem;
  z-index: 200;

  /* 信笺标签外观 */
  background: linear-gradient(135deg, #C4A77D 0%, #B89A6B 100%);
  color: #3D3225;
  border: none;
  border-radius: 6px 0 0 6px;
  padding: 0.6rem 0.75rem;

  /* 宋体字体 */
  font-family: "Songti SC", "Songti TC", "STSong", "SimSun", "宋体", serif;
  
  /* 文字横排 */
  font-size: 0.875rem;
  font-weight: 500;
  letter-spacing: 0.1em;
  
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
  -webkit-appearance: none;
  appearance: none;
  box-shadow: -2px 2px 8px rgba(0, 0, 0, 0.15);
  transition: all 0.3s ease;
}

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

.index-tab:hover {
  background: linear-gradient(135deg, #D4B78D 0%, #C8AA7B 100%);
  padding-right: 1rem;
  box-shadow: -3px 3px 12px rgba(0, 0, 0, 0.2);
}

.index-tab.is-active {
  background: linear-gradient(135deg, #A08050 0%, #8F7340 100%);
  color: #F5F0E8;
  /* 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: "Kaiti SC", "Kaiti TC", "STKaiti", "KaiTi", "楷体", serif;
  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", 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;
}

/* ── 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; }

  .layout {
    padding: 0;
  }

  .paper {
    padding: 1.5rem 1.25rem 3rem;
    border-right: none;
    box-shadow: none;
  }

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

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

  /* 移动端标签调整 */
  .index-tab {
    padding: 0.5rem 0.6rem;
    font-size: 0.8rem;
    top: 4rem;
  }

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

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

/* ============================================================
   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;
}