/* ============================================================
   Statistics & Data Science: A Visual Handbook
   Shared Stylesheet — John Fisher 2026
   ============================================================ */

@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700;800;900&family=JetBrains+Mono:wght@400;500&family=Playfair+Display:ital,wght@0,700;1,700&display=swap');

/* ---------- CSS Custom Properties ---------- */
:root {
  --navy:       #050b1f;
  --navy-2:     #0d1535;
  --navy-3:     #131c3e;
  --card-bg:    rgba(255,255,255,0.04);
  --card-border:rgba(255,255,255,0.08);
  --cyan:       #00d4ff;
  --cyan-dim:   #00a8cc;
  --purple:     #7c3aed;
  --purple-dim: #5b21b6;
  --amber:      #f59e0b;
  --green:      #10b981;
  --red:        #ef4444;
  --text:       #e8eaf6;
  --text-dim:   #a6afce;   /* lightened for stronger contrast on the navy background */
  --text-muted: #7e89af;   /* lightened: was #4a5568 (too dark to read on navy) */
  --border:     rgba(255,255,255,0.07);
  --radius:     12px;
  --radius-lg:  20px;
  --transition: all 0.25s cubic-bezier(0.4,0,0.2,1);
  --shadow-glow: 0 0 40px rgba(0,212,255,0.15);
  --font-mono:  'JetBrains Mono', monospace;
}

/* ---------- Reset ---------- */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: 'Inter', system-ui, sans-serif;
  background: var(--navy);
  color: var(--text);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}
a { color: var(--cyan); text-decoration: none; transition: var(--transition); }
a:hover { color: #fff; }
img { max-width: 100%; display: block; }

/* ---------- Utility ---------- */
.gradient-text {
  background: linear-gradient(135deg, var(--cyan) 0%, #a78bfa 50%, var(--amber) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}
.glass {
  background: var(--card-bg);
  border: 1px solid var(--card-border);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
}
.tag {
  display: inline-flex; align-items: center; gap: 4px;
  font-size: 0.7rem; font-weight: 600; letter-spacing: 0.08em;
  text-transform: uppercase; padding: 3px 10px;
  border-radius: 100px; border: 1px solid;
}
.tag-cyan  { color: var(--cyan);   border-color: rgba(0,212,255,0.3);   background: rgba(0,212,255,0.08); }
.tag-new   { color: var(--amber);  border-color: rgba(245,158,11,0.3);  background: rgba(245,158,11,0.08);}
.tag-purple{ color: #a78bfa;       border-color: rgba(167,139,250,0.3); background: rgba(167,139,250,0.08);}

/* ---------- Scrollbar ---------- */
::-webkit-scrollbar { width: 6px; height: 6px; }
::-webkit-scrollbar-track { background: var(--navy-2); }
::-webkit-scrollbar-thumb { background: var(--purple-dim); border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: var(--purple); }

/* ---------- Nav Bar (shared) ---------- */
.topnav {
  position: fixed; top: 0; left: 0; right: 0; z-index: 1000;
  display: flex; align-items: center; justify-content: space-between;
  padding: 0 2rem; height: 60px;
  background: rgba(5,11,31,0.85);
  border-bottom: 1px solid var(--border);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
}
.topnav .logo {
  font-weight: 800; font-size: 0.8rem; letter-spacing: 0.01em;
  color: var(--text); display: flex; align-items: center; gap: 9px; white-space: nowrap;
}
.topnav .logo .ai { color: var(--cyan); }
.topnav .nav-links { display: flex; gap: 1.5rem; align-items: center; }
.topnav .nav-links a {
  color: var(--text-dim); font-size: 0.85rem; font-weight: 500;
  transition: var(--transition);
}
.topnav .nav-links a:hover,
.topnav .nav-links a.active { color: var(--cyan); }

/* ---------- Buttons ---------- */
.btn {
  display: inline-flex; align-items: center; gap: 8px;
  padding: 0.7rem 1.6rem; border-radius: 8px;
  font-weight: 600; font-size: 0.9rem; cursor: pointer;
  border: none; transition: var(--transition); text-decoration: none;
}
.btn-primary {
  background: linear-gradient(135deg, var(--cyan) 0%, var(--purple) 100%);
  color: #fff;
  box-shadow: 0 4px 20px rgba(0,212,255,0.3);
}
.btn-primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 8px 30px rgba(0,212,255,0.5);
  color: #fff;
}
.btn-ghost {
  background: var(--card-bg); color: var(--text);
  border: 1px solid var(--card-border);
}
.btn-ghost:hover { background: rgba(255,255,255,0.08); color: #fff; }

/* ---------- Footer ---------- */
.book-footer {
  text-align: center; padding: 2.5rem 2rem;
  color: var(--text-muted); font-size: 0.8rem;
  border-top: 1px solid var(--border);
}
.book-footer strong { color: var(--text-dim); }