/* ── SQL / 数据库 Tutorial — Database-Inspired Design ── */
:root {
  --pg-blue: #336791;
  --pg-blue-light: #4A90D9;
  --pg-blue-faint: #EBF4FB;
  --sql-teal: #1ABC9C;
  --sql-teal-light: #E8F8F5;
  --dark: #1A2332;
  --dark-surface: #243447;
  --text: #1A2332;
  --text-secondary: #3D5A7A;
  --text-muted: #7A96B0;
  --paper: #F8FAFD;
  --paper-warm: #F0F4F8;
  --border: #D4E2EF;
  --border-dark: #A8C0D4;
  --row-even: #F0F8FF;
  --row-odd: #FFFFFF;
  --header-bg: #336791;
  --header-text: #FFFFFF;
  --mono: 'SF Mono', 'Fira Code', Consolas, monospace;
  --radius: 8px;
  --radius-lg: 12px;
  --orange: #E67E22;
  --red: #E74C3C;
  --green: #27AE60;
}

* { margin: 0; padding: 0; box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  font-family: -apple-system, 'Inter', 'Segoe UI', sans-serif;
  background: var(--paper);
  color: var(--text);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

/* NAV */
.nav {
  position: sticky; top: 0; z-index: 100;
  background: var(--dark); border-bottom: 1px solid rgba(255,255,255,0.08);
  padding: 0 24px; height: 52px; display: flex; align-items: center; gap: 16px;
}
.nav-back { color: #7FB9E0; text-decoration: none; font-size: 0.88rem; display: flex; align-items: center; gap: 4px; }
.nav-back::before { content: '‹'; font-size: 1.3rem; }
.nav-title { font-size: 0.92rem; font-weight: 600; flex: 1; color: #E8F4FF; }
.nav-badge { background: var(--pg-blue); color: #fff; font-size: 0.65rem; font-weight: 700; padding: 3px 10px; border-radius: 20px; }

/* HERO */
.hero {
  background: linear-gradient(160deg, var(--dark) 0%, #1E3A5F 50%, var(--dark-surface) 100%);
  color: #fff; padding: 80px 24px 70px; text-align: center; position: relative; overflow: hidden;
}
.hero::before {
  content: ''; position: absolute; inset: 0; opacity: 0.04;
  background-image: repeating-linear-gradient(0deg, transparent, transparent 39px, rgba(255,255,255,1) 39px, rgba(255,255,255,1) 40px),
    repeating-linear-gradient(90deg, transparent, transparent 39px, rgba(255,255,255,1) 39px, rgba(255,255,255,1) 40px);
}
.hero-icon { font-size: 3.5rem; margin-bottom: 14px; position: relative; display: inline-block; }
.hero-eyebrow { font-family: var(--mono); font-size: 0.7rem; letter-spacing: 0.2em; text-transform: uppercase; color: #7FB9E0; margin-bottom: 12px; position: relative; }
.hero h1 { font-size: clamp(2rem, 5vw, 3.2rem); font-weight: 700; letter-spacing: -0.02em; position: relative; margin-bottom: 16px; }
.hero-sub { font-size: 0.98rem; color: rgba(255,255,255,0.62); max-width: 520px; margin: 0 auto 28px; position: relative; }
.hero-chips { display: flex; flex-wrap: wrap; gap: 8px; justify-content: center; position: relative; }
.chip { background: rgba(255,255,255,0.08); border: 1px solid rgba(255,255,255,0.16); color: rgba(255,255,255,0.72); font-size: 0.75rem; padding: 4px 12px; border-radius: 20px; font-family: var(--mono); }

/* CONTAINER */
.container { max-width: 860px; margin: 0 auto; padding: 36px 24px 80px; }

/* CARDS */
.card { background: #fff; border: 1px solid var(--border); border-radius: var(--radius-lg); padding: 22px; margin-bottom: 14px; box-shadow: 0 1px 4px rgba(0,0,0,0.04); }
.card-list { list-style: none; }
.card-list li { border-bottom: 1px solid var(--border); }
.card-list li:last-child { border-bottom: none; }
.card-list a { display: flex; align-items: flex-start; gap: 14px; padding: 14px 10px; text-decoration: none; color: inherit; border-radius: var(--radius); transition: background 0.15s; }
.card-list a:hover { background: var(--pg-blue-faint); }
.list-num { width: 28px; height: 28px; background: var(--pg-blue); color: #fff; border-radius: 50%; display: flex; align-items: center; justify-content: center; font-size: 0.72rem; font-weight: 700; flex-shrink: 0; font-family: var(--mono); }
.list-content { flex: 1; }
.list-title { font-size: 0.93rem; font-weight: 600; color: var(--text); margin-bottom: 3px; }
.list-desc { font-size: 0.8rem; color: var(--text-muted); }
.list-chevron { color: var(--border-dark); font-size: 1rem; align-self: center; }
.section-label { font-size: 0.68rem; font-weight: 700; letter-spacing: 0.14em; text-transform: uppercase; color: var(--text-muted); margin: 30px 0 10px 2px; }

/* CHAPTER PAGE */
.chapter-hero { background: linear-gradient(135deg, var(--pg-blue) 0%, #1E5C9E 100%); color: #fff; padding: 56px 24px 48px; text-align: center; }
.chapter-hero .ch-num { font-size: 0.68rem; letter-spacing: 0.22em; text-transform: uppercase; color: rgba(255,255,255,0.6); margin-bottom: 10px; font-family: var(--mono); }
.chapter-hero h1 { font-size: clamp(1.7rem, 4vw, 2.5rem); font-weight: 700; margin-bottom: 12px; }
.chapter-hero p { color: rgba(255,255,255,0.75); font-size: 0.93rem; max-width: 520px; margin: 0 auto; }

/* CONTENT */
.content { max-width: 760px; margin: 0 auto; padding: 44px 24px 80px; }
h2 { font-size: 1.35rem; font-weight: 700; color: var(--text); margin: 44px 0 14px; padding-bottom: 10px; border-bottom: 2px solid var(--pg-blue-faint); }
h2:first-child { margin-top: 0; }
h3 { font-size: 1.05rem; font-weight: 700; color: var(--text); margin: 28px 0 10px; }
h4 { font-size: 0.72rem; font-weight: 700; letter-spacing: 0.1em; text-transform: uppercase; color: var(--text-muted); margin: 18px 0 8px; }
p { margin-bottom: 14px; color: var(--text-secondary); font-size: 0.93rem; line-height: 1.8; }

/* Callouts */
.callout { border-radius: var(--radius); padding: 14px 16px; margin: 18px 0; display: flex; gap: 12px; align-items: flex-start; font-size: 0.87rem; line-height: 1.65; }
.callout-icon { font-size: 1rem; flex-shrink: 0; margin-top: 2px; }
.callout p { margin: 0; color: inherit; font-size: inherit; }
.callout strong { display: block; margin-bottom: 3px; font-weight: 700; }
.callout.info { background: var(--pg-blue-faint); color: #1A3C5E; border-left: 3px solid var(--pg-blue); }
.callout.tip { background: var(--sql-teal-light); color: #0E4030; border-left: 3px solid var(--sql-teal); }
.callout.warning { background: #FEF9E7; color: #7D4A0A; border-left: 3px solid var(--orange); }
.callout.danger { background: #FDEDEC; color: #7B1C1C; border-left: 3px solid var(--red); }

/* DB Table visualization */
.db-table { width: 100%; border-collapse: collapse; margin: 16px 0; font-size: 0.86rem; border-radius: var(--radius); overflow: hidden; box-shadow: 0 2px 8px rgba(51,103,145,0.12); }
.db-table thead tr { background: var(--header-bg); }
.db-table thead th { color: var(--header-text); font-weight: 700; padding: 11px 16px; text-align: left; font-size: 0.8rem; letter-spacing: 0.03em; }
.db-table tbody tr:nth-child(even) { background: var(--row-even); }
.db-table tbody tr:nth-child(odd) { background: var(--row-odd); }
.db-table td { padding: 10px 16px; color: var(--text-secondary); border-bottom: 1px solid var(--border); }
.db-table tbody tr:last-child td { border-bottom: none; }
.db-table .pk { color: var(--pg-blue); font-weight: 700; font-family: var(--mono); }
.db-table .fk { color: var(--sql-teal); font-family: var(--mono); }

/* General table */
table { width: 100%; border-collapse: collapse; margin: 18px 0; font-size: 0.86rem; }
th { background: var(--paper-warm); color: var(--text); font-weight: 700; padding: 10px 14px; text-align: left; font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.06em; border-bottom: 2px solid var(--border-dark); }
td { padding: 10px 14px; border-top: 1px solid var(--border); color: var(--text-secondary); }

/* Code */
pre { background: var(--dark); color: #E8F4FF; border-radius: var(--radius); padding: 18px 20px; overflow-x: auto; font-size: 0.84rem; line-height: 1.7; margin: 14px 0; position: relative; }
pre .lang-label { position: absolute; top: 8px; right: 12px; font-size: 0.6rem; font-weight: 700; letter-spacing: 0.1em; text-transform: uppercase; color: rgba(255,255,255,0.25); }
code { font-family: var(--mono); }
p code, li code, td code { background: var(--pg-blue-faint); color: var(--pg-blue); padding: 2px 6px; border-radius: 4px; font-size: 0.85em; }
/* SQL syntax */
.kw { color: #88CCFF; font-weight: 700; }  /* SQL keywords: SELECT/FROM/WHERE */
.ty { color: #7FD8FC; }
.st { color: #A8E87F; }
.cm { color: #5A7A9A; font-style: italic; }
.fn { color: #FFD080; }
.nu { color: #FF9F80; }
.at { color: #80FFCF; }
.op { color: #FF88AA; }  /* operators */
.tb { color: #FFB86C; }  /* table names */

/* Def list */
.def-list { list-style: none; }
.def-list li { padding: 12px 0; border-bottom: 1px solid var(--border); display: grid; grid-template-columns: 160px 1fr; gap: 16px; font-size: 0.88rem; }
.def-list li:last-child { border-bottom: none; }
.def-term { font-weight: 700; color: var(--pg-blue); font-family: var(--mono); font-size: 0.83rem; }
.def-desc { color: var(--text-secondary); }

/* Progress */
.progress { height: 4px; background: var(--border); border-radius: 2px; margin-bottom: 32px; }
.progress-bar { height: 100%; background: linear-gradient(90deg, var(--pg-blue), var(--sql-teal)); border-radius: 2px; }

.two-col { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; margin: 14px 0; }
.content ul, .content ol { padding-left: 22px; margin: 10px 0 14px; color: var(--text-secondary); font-size: 0.91rem; line-height: 1.85; }

/* Chapter nav */
.chapter-nav { display: flex; gap: 12px; margin-top: 48px; padding-top: 22px; border-top: 1px solid var(--border); }
.chapter-nav a { flex: 1; display: flex; flex-direction: column; gap: 4px; padding: 14px; background: #fff; border: 1px solid var(--border); border-radius: var(--radius); text-decoration: none; color: inherit; transition: border-color 0.2s; box-shadow: 0 1px 3px rgba(0,0,0,0.04); }
.chapter-nav a:hover { border-color: var(--pg-blue); }
.nav-dir { font-size: 0.7rem; color: var(--text-muted); text-transform: uppercase; letter-spacing: 0.1em; }
.nav-title-text { font-weight: 600; color: var(--pg-blue); font-size: 0.88rem; }
.prev { text-align: left; } .next { text-align: right; }

.overview-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(220px, 1fr)); gap: 12px; margin: 14px 0; }
.overview-card { background: var(--paper-warm); border: 1px solid var(--border); border-radius: var(--radius); padding: 16px; }
.overview-card .ov-icon { font-size: 1.4rem; margin-bottom: 8px; }
.overview-card h3 { font-size: 0.88rem; margin: 0 0 5px; }
.overview-card p { font-size: 0.78rem; margin: 0; color: var(--text-muted); line-height: 1.5; }
@media (max-width: 600px) { .two-col { grid-template-columns: 1fr; } .def-list li { grid-template-columns: 1fr; } }

.site-footer { border-top: 1px solid var(--border); padding: 28px 24px; text-align: center; font-size: 0.78rem; color: var(--text-muted); background: var(--paper-warm); }
.site-footer a { color: var(--pg-blue); text-decoration: none; }