/* ===== 约束理论（TOC）网站 · 共享样式（原创） ===== */
:root {
  --primary: #1f4e8c;
  --primary-dark: #163a68;
  --accent: #e8a33d;
  --ink: #16233a;
  --text: #2c3a4d;
  --muted: #64748b;
  --bg: #f7f9fc;
  --card: #ffffff;
  --line: #e2e8f0;
  --radius: 12px;
  --shadow: 0 2px 10px rgba(22, 35, 58, .08);
  --font: "PingFang SC", "Microsoft YaHei", "Noto Sans SC", "Source Han Sans SC", system-ui, -apple-system, sans-serif;
}
* { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body { font-family: var(--font); color: var(--text); background: var(--bg); line-height: 1.7; }
a { color: var(--primary); text-decoration: none; }
a:hover { text-decoration: underline; }
img, svg { max-width: 100%; }

.container { max-width: 1120px; margin: 0 auto; padding: 0 20px; }

/* ---- 顶部导航 ---- */
.site-header { position: sticky; top: 0; z-index: 50; background: rgba(255,255,255,.95); backdrop-filter: blur(6px); border-bottom: 1px solid var(--line); }
.site-header .container { display: flex; align-items: center; gap: 24px; height: 60px; }
.brand { font-size: 20px; font-weight: 700; color: var(--ink); white-space: nowrap; }
.brand:hover { text-decoration: none; }
.brand .toc-badge { font-size: 12px; color: #fff; background: var(--primary); border-radius: 4px; padding: 1px 6px; margin-left: 6px; vertical-align: middle; }
.main-nav { display: flex; gap: 20px; margin-left: auto; align-items: center; }
.main-nav a { color: var(--text); font-size: 15px; }
.main-nav a:hover { color: var(--primary); text-decoration: none; }
.btn { display: inline-block; border: none; cursor: pointer; font-family: inherit; font-size: 15px; border-radius: 8px; padding: 8px 18px; transition: background .15s, color .15s; }
.btn-primary { background: var(--primary); color: #fff; }
.btn-primary:hover { background: var(--primary-dark); text-decoration: none; }
.btn-ghost { background: transparent; color: var(--primary); border: 1px solid var(--primary); }
.btn-ghost:hover { background: var(--primary); color: #fff; text-decoration: none; }
.btn-sm { padding: 5px 12px; font-size: 14px; }
.user-chip { display: flex; align-items: center; gap: 10px; font-size: 14px; color: var(--ink); }

/* ---- 通用区块 ---- */
.section { padding: 64px 0; }
.section-title { font-size: 30px; color: var(--ink); text-align: center; margin-bottom: 8px; }
.section-sub { text-align: center; color: var(--muted); max-width: 720px; margin: 0 auto 40px; }
.card { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); box-shadow: var(--shadow); }

/* ---- 页脚 ---- */
.site-footer { background: var(--ink); color: #aebdd0; padding: 40px 0 24px; font-size: 14px; }
.site-footer a { color: #cfd9e6; }
.site-footer .footer-grid { display: grid; grid-template-columns: 2fr 1fr 1fr; gap: 32px; margin-bottom: 24px; }
.site-footer h4 { color: #fff; font-size: 15px; margin-bottom: 10px; }
.site-footer .copyright { border-top: 1px solid rgba(255,255,255,.12); padding-top: 16px; text-align: center; color: #7f92a9; }

/* ---- 登录/注册弹窗 ---- */
.modal-mask { position: fixed; inset: 0; background: rgba(15,25,40,.5); display: none; align-items: center; justify-content: center; z-index: 100; }
.modal-mask.open { display: flex; }
.modal { background: #fff; border-radius: var(--radius); width: 380px; max-width: 92vw; padding: 28px; box-shadow: 0 12px 40px rgba(0,0,0,.2); }
.modal h3 { color: var(--ink); margin-bottom: 18px; text-align: center; }
.modal .field { margin-bottom: 14px; }
.modal label { display: block; font-size: 14px; color: var(--muted); margin-bottom: 4px; }
.modal input { width: 100%; padding: 9px 12px; border: 1px solid var(--line); border-radius: 8px; font-size: 15px; font-family: inherit; }
.modal input:focus { outline: 2px solid rgba(31,78,140,.35); border-color: var(--primary); }
.modal .error { color: #c0392b; font-size: 13px; min-height: 20px; margin: 6px 0; }
.modal .switch { text-align: center; font-size: 14px; margin-top: 12px; color: var(--muted); }
.modal .close-x { float: right; cursor: pointer; color: var(--muted); font-size: 20px; line-height: 1; border: none; background: none; }
.modal .btn-block { width: 100%; padding: 10px; }

/* ---- 提示条 ---- */
.toast { position: fixed; left: 50%; bottom: 32px; transform: translateX(-50%); background: var(--ink); color: #fff; padding: 10px 22px; border-radius: 8px; font-size: 14px; opacity: 0; transition: opacity .25s; z-index: 200; pointer-events: none; }
.toast.show { opacity: .95; }

/* ---- 响应式 ---- */
@media (max-width: 768px) {
  .main-nav { gap: 12px; font-size: 14px; }
  .main-nav a.hide-m { display: none; }
  .site-footer .footer-grid { grid-template-columns: 1fr; }
  .section { padding: 44px 0; }
  .section-title { font-size: 24px; }
}