/* ============================================================
   入世山房 · 基础样式
   设计基调:墨黑宣纸朱砂,留白如水,印章落款
   ============================================================ */

/* ---------- 设计令牌 ---------- */
:root {
  /* 墨色系 */
  --ink-900: #1a1612;
  --ink-700: #3a322b;
  --ink-500: #6b6056;
  --ink-300: #a89e90;
  --ink-100: #d6cfc2;

  /* 宣纸 */
  --paper-50:  #fbf8f1;
  --paper-100: #f5f0e3;
  --paper-200: #ebe3cf;
  --paper-300: #ddd2b3;

  /* 朱砂 / 点睛 */
  --cinnabar: #b8332a;
  --cinnabar-deep: #8a1f1a;

  /* 远山青 */
  --mountain: #5a6b5d;
  --mountain-deep: #3a4a3d;

  /* 赭石 / 暖辅 */
  --ochre: #a86c4d;

  /* 间距尺度(8 倍数) */
  --s-1: 8px;
  --s-2: 16px;
  --s-3: 24px;
  --s-4: 32px;
  --s-5: 48px;
  --s-6: 72px;
  --s-7: 112px;
  --s-8: 160px;

  /* 字号尺度 */
  --t-xs: 12px;
  --t-sm: 14px;
  --t-base: 16px;
  --t-md: 18px;
  --t-lg: 22px;
  --t-xl: 28px;
  --t-2xl: 36px;
  --t-3xl: 52px;
  --t-4xl: 72px;

  /* 字距 */
  --tracking-wide: 0.4em;
  --tracking-base: 0.16em;

  /* 阴影 */
  --shadow-paper: 0 1px 0 rgba(58, 50, 43, 0.04),
                  0 12px 32px -16px rgba(58, 50, 43, 0.12);
}

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

html {
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-family: "Noto Serif SC", "Source Han Serif SC", "Songti SC",
    "STSong", "SimSun", serif;
  font-size: var(--t-base);
  line-height: 1.8;
  color: var(--ink-700);
  background: var(--paper-50);
  /* 宣纸纹理(极轻) */
  background-image:
    radial-gradient(circle at 20% 10%, rgba(168, 110, 77, 0.04) 0, transparent 40%),
    radial-gradient(circle at 80% 80%, rgba(90, 107, 93, 0.04) 0, transparent 40%);
}

img, svg {
  display: block;
  max-width: 100%;
}

a {
  color: inherit;
  text-decoration: none;
}

button {
  font-family: inherit;
  border: none;
  background: none;
  cursor: pointer;
  color: inherit;
}

/* ---------- 排版工具 ---------- */
.serif-display {
  font-family: "Noto Serif SC", "Source Han Serif SC", "Songti SC", serif;
  font-weight: 500;
  letter-spacing: var(--tracking-base);
}

.label-min {
  font-size: var(--t-xs);
  letter-spacing: var(--tracking-wide);
  color: var(--ink-500);
  text-transform: uppercase;
}

.text-cinnabar { color: var(--cinnabar); }
.text-mountain { color: var(--mountain-deep); }

/* 容器 */
.container {
  width: 100%;
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 var(--s-4);
}

.container-narrow {
  max-width: 760px;
}

/* 章节通栏 */
.section {
  padding: var(--s-7) 0;
}

.section-tight {
  padding: var(--s-5) 0;
}

@media (max-width: 720px) {
  .section { padding: var(--s-5) 0; }
  :root {
    --t-3xl: 36px;
    --t-4xl: 48px;
    --s-7: 72px;
  }
}

/* ---------- 顶部导航 ---------- */
.nav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(251, 248, 241, 0.85);
  backdrop-filter: saturate(140%) blur(12px);
  -webkit-backdrop-filter: saturate(140%) blur(12px);
  border-bottom: 1px solid rgba(58, 50, 43, 0.06);
}

.nav-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 72px;
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 var(--s-4);
}

.brand-mark {
  display: flex;
  align-items: center;
  gap: var(--s-2);
}

.brand-seal {
  width: 40px;
  height: 40px;
  display: grid;
  place-items: center;
  background: var(--cinnabar);
  color: var(--paper-50);
  font-family: "Noto Serif SC", "Songti SC", serif;
  font-weight: 700;
  font-size: 20px;
  letter-spacing: 0;
  /* 印章风格 */
  box-shadow:
    inset 0 0 0 2px var(--paper-50),
    inset 0 0 0 3px var(--cinnabar);
  border-radius: 2px;
  flex-shrink: 0;
}

.brand-text {
  display: flex;
  flex-direction: column;
  line-height: 1.1;
}

.brand-name {
  font-size: var(--t-md);
  font-weight: 600;
  color: var(--ink-900);
  letter-spacing: 0.1em;
}

.brand-sub {
  font-size: 11px;
  color: var(--ink-500);
  letter-spacing: var(--tracking-base);
  margin-top: 2px;
}

.nav-links {
  display: flex;
  gap: var(--s-5);
  list-style: none;
}

.nav-links a {
  font-size: var(--t-sm);
  letter-spacing: 0.2em;
  color: var(--ink-700);
  position: relative;
  padding: 4px 0;
  transition: color 0.2s;
}

.nav-links a:hover,
.nav-links a.active {
  color: var(--cinnabar);
}

.nav-links a.active::after {
  content: "";
  position: absolute;
  left: 50%;
  bottom: -8px;
  width: 4px;
  height: 4px;
  background: var(--cinnabar);
  border-radius: 50%;
  transform: translateX(-50%);
}

/* 移动端菜单按钮 */
.nav-toggle {
  display: none;
  width: 32px;
  height: 32px;
  align-items: center;
  justify-content: center;
}

.nav-toggle span {
  display: block;
  width: 18px;
  height: 1px;
  background: var(--ink-900);
  position: relative;
}

.nav-toggle span::before,
.nav-toggle span::after {
  content: "";
  position: absolute;
  left: 0;
  width: 100%;
  height: 1px;
  background: var(--ink-900);
}

.nav-toggle span::before { top: -6px; }
.nav-toggle span::after { top: 6px; }

@media (max-width: 720px) {
  .nav-links {
    position: fixed;
    inset: 72px 0 auto 0;
    flex-direction: column;
    background: var(--paper-50);
    padding: var(--s-4);
    gap: var(--s-3);
    border-bottom: 1px solid var(--paper-200);
    transform: translateY(-110%);
    transition: transform 0.25s;
  }

  .nav-links.open { transform: translateY(0); }
  .nav-toggle { display: flex; }
}

/* ---------- 页脚 ---------- */
.footer {
  margin-top: var(--s-7);
  padding: var(--s-5) 0 var(--s-3);
  border-top: 1px solid var(--paper-200);
  background: var(--paper-100);
}

.footer-grid {
  display: grid;
  grid-template-columns: 1.4fr 1fr 1fr 1fr;
  gap: var(--s-5);
  margin-bottom: var(--s-5);
}

@media (max-width: 720px) {
  .footer-grid {
    grid-template-columns: 1fr 1fr;
    gap: var(--s-4);
  }
}

.footer h4 {
  font-size: var(--t-sm);
  font-weight: 600;
  color: var(--ink-900);
  margin-bottom: var(--s-2);
  letter-spacing: 0.1em;
}

.footer p,
.footer li {
  font-size: var(--t-sm);
  color: var(--ink-500);
  line-height: 2;
  list-style: none;
}

.footer-brand {
  display: flex;
  flex-direction: column;
  gap: var(--s-2);
}

.footer-brand .slogan {
  font-style: italic;
  color: var(--ink-700);
  font-size: var(--t-md);
  letter-spacing: 0.1em;
}

.footer-bottom {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding-top: var(--s-3);
  border-top: 1px solid var(--paper-200);
  font-size: var(--t-xs);
  color: var(--ink-500);
  letter-spacing: 0.1em;
}

@media (max-width: 720px) {
  .footer-bottom {
    flex-direction: column;
    gap: var(--s-1);
    text-align: center;
  }
}

/* ---------- 通用:印章元素 ---------- */
.seal {
  display: inline-grid;
  place-items: center;
  background: var(--cinnabar);
  color: var(--paper-50);
  padding: 4px 10px;
  font-size: var(--t-xs);
  font-weight: 700;
  letter-spacing: 0.2em;
  border-radius: 2px;
  box-shadow:
    inset 0 0 0 1px var(--paper-50),
    inset 0 0 0 2px var(--cinnabar);
}

/* 落款竖排 */
.vertical-seal {
  writing-mode: vertical-rl;
  font-family: "Noto Serif SC", serif;
  letter-spacing: 0.4em;
  color: var(--cinnabar);
}

/* ---------- 通用:按钮 ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--s-1);
  padding: 14px 28px;
  font-size: var(--t-sm);
  letter-spacing: 0.2em;
  border-radius: 2px;
  transition: all 0.25s;
  cursor: pointer;
}

.btn-primary {
  background: var(--ink-900);
  color: var(--paper-50);
}

.btn-primary:hover {
  background: var(--cinnabar);
}

.btn-ghost {
  background: transparent;
  color: var(--ink-900);
  border: 1px solid var(--ink-900);
}

.btn-ghost:hover {
  background: var(--ink-900);
  color: var(--paper-50);
}

/* ---------- 通用:章节标题 ---------- */
.section-title {
  text-align: center;
  margin-bottom: var(--s-6);
}

.section-title .label {
  font-size: var(--t-xs);
  letter-spacing: var(--tracking-wide);
  color: var(--cinnabar);
  margin-bottom: var(--s-2);
}

.section-title h2 {
  font-size: var(--t-3xl);
  font-weight: 500;
  color: var(--ink-900);
  letter-spacing: 0.2em;
  margin-bottom: var(--s-2);
}

.section-title .desc {
  font-size: var(--t-md);
  color: var(--ink-500);
  letter-spacing: 0.1em;
  font-style: italic;
}

@media (max-width: 720px) {
  .section-title h2 { font-size: var(--t-2xl); }
}