/* Modern NCE UI — Apple-inspired, minimal, adaptive */
:root {
  --bg: #0a0a0c;
  --surface: #0f1014;
  --card: #14161b;
  --text: #e7e7ea;
  --muted: #a1a1a7;
  --border: rgba(255,255,255,0.08);
  --shadow: 0 10px 30px rgba(0,0,0,0.4);
  --accent: #0a84ff; /* iOS Blue */
  --accent-2: #7c4dff; /* purple */
  --radius: 14px;
}

@media (prefers-color-scheme: light) {
  :root { --bg:#f5f5f7; --surface:#f8f8fa; --card:#ffffff; --text:#1d1d1f; --muted:#6e6e73; --border:rgba(0,0,0,0.08); --shadow:0 12px 30px rgba(0,0,0,0.08);} 
}

*{box-sizing:border-box}
html,body{height:100%}
body{
  margin:0;
  font-family:-apple-system,BlinkMacSystemFont,"SF Pro Text","SF Pro Display","Helvetica Neue",Arial,"Microsoft YaHei",sans-serif;
  color:var(--text);
  background: linear-gradient(180deg,
               color-mix(in srgb, var(--bg) 98%, var(--accent) 2%),
               color-mix(in srgb, var(--bg) 98%, var(--accent-2) 2%)) fixed;
}

/* Subtle animated ambient layer with smooth fade-in */
body::before{
  content:""; position:fixed; inset:0; pointer-events:none; z-index:-1;
  background: radial-gradient(900px 600px at 15% 5%, color-mix(in srgb, var(--accent) 10%, transparent), transparent 60%),
              radial-gradient(900px 600px at 85% 0%, color-mix(in srgb, var(--accent-2) 8%, transparent), transparent 60%);
  opacity:0; animation: bgFade .9s ease-out forwards;
}

@keyframes bgFade { from { opacity:0 } to { opacity:.8 } }

@media (prefers-reduced-motion: reduce){
  body::before{ animation: none; opacity:.6 }
}

.container{max-width:1120px;margin:0 auto;padding:0 18px}

/* Header / Hero */
.hero{padding:48px 0 20px;text-align:center}
.hero .brand{font-size:12px;color:var(--muted);letter-spacing:.08em;text-transform:uppercase;margin-bottom:6px}
.hero h1{font-size:48px;line-height:1.06;letter-spacing:-.02em;margin:0 0 8px;
  background: linear-gradient(90deg, color-mix(in srgb, var(--text) 85%, var(--accent) 15%), color-mix(in srgb, var(--accent-2) 50%, var(--text) 50%));
  -webkit-background-clip:text; background-clip:text; color:transparent;
}
.hero p{color:var(--muted);margin:0;font-size:14px}
.hero .subtitle{margin-top:6px;margin-bottom:10px;font-size:13px;color:var(--muted);letter-spacing:0.02em}
/* badges removed per design feedback */

/* Back button inline with player */
.back-inline{display:inline-flex;align-items:center;gap:6px;padding:6px 10px;border-radius:999px;border:1px solid var(--border);background:var(--surface);box-shadow:var(--shadow);color:inherit;flex:0 0 auto;}
.back-inline svg{width:14px;height:14px;fill:currentColor}

/* Segmented control */
.segmented{display:inline-flex;gap:6px;background:color-mix(in srgb, var(--bg) 70%, transparent);border:1px solid var(--border);border-radius:999px;padding:4px;margin-top:14px;backdrop-filter:saturate(120%) blur(10px)}
.segmented .seg{appearance:none;border:0;background:transparent;color:var(--text);font-size:12px;padding:8px 12px;border-radius:999px;cursor:pointer;text-decoration:none;transition:background .15s ease, color .15s ease}
.segmented .seg.active{background:color-mix(in srgb, var(--accent) 20%, var(--card));box-shadow:var(--shadow)}
/* tiny segmented for minimal toolbar switches */
.segmented.tiny{padding:2px;gap:2px}
.segmented.tiny .seg{font-size:11px;padding:6px 8px}

/* Smaller top tabs for book switch */
.segmented.tabs{padding:4px; gap:6px; margin-top:14px}
.segmented.tabs .seg{font-size:12px; padding:8px 12px}

@media (max-width: 768px){
  .hero{padding:36px 0 16px}
  .hero h1{font-size:40px}
  .segmented.tabs .seg{font-size:12px; padding:8px 12px}
}

/* Book cards grid */
.grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(260px,1fr));gap:18px;padding:26px 0 64px}
.card{position:relative;border:1px solid var(--border);background:var(--surface);border-radius:var(--radius);box-shadow:var(--shadow);overflow:hidden;transition:transform .2s ease, box-shadow .2s ease}
.card:hover{transform:translateY(-4px)}
.card img{width:100%;height:160px;object-fit:cover;display:block;opacity:.9}
.card .body{padding:14px 14px 16px}
.card .title{font-weight:700;margin:6px 0 4px}
.card .sub{font-size:12px;color:var(--muted)}

/* Lessons grid */
.lessons{display:grid;grid-template-columns:repeat(auto-fit,minmax(280px,1fr));gap:12px;padding:10px 0 40px}
.lesson-item{border:1px solid var(--border);background:var(--surface);border-radius:var(--radius);box-shadow:var(--shadow);padding:14px 16px;display:flex;gap:10px;align-items:center;color:inherit;text-decoration:none;transition:transform .15s ease}
.lesson-item:hover{transform:translateY(-2px)}
.lesson-num{font-weight:700;color:var(--accent)}

/* Lesson page */
.toolbar{position:sticky;top:0;z-index:10;background:transparent;padding:6px 0 4px;border-bottom:none}
.toolbar .row{display:flex;align-items:center;justify-content:flex-end;gap:10px}
.toolbar .info{display:flex;align-items:center;gap:10px}
.toolbar .title{font-weight:700}
.toolbar .sub{font-size:12px;color:var(--muted)}
.controls{display:flex;align-items:center;gap:8px}
.btn{appearance:none;border:1px solid var(--border);background:color-mix(in srgb, var(--card) 90%, transparent);backdrop-filter:saturate(120%) blur(10px);color:inherit;border-radius:10px;padding:6px 10px;cursor:pointer}
.btn:hover{transform:translateY(-1px)}

.sentences{padding:12px 0 22px}
.sentence{border:1px solid var(--border);background:var(--surface);border-radius:var(--radius);box-shadow:var(--shadow);padding:12px 14px;margin:10px 0;cursor:pointer;transition:transform .12s ease}
.sentence:hover{transform:translateY(-2px)}
.sentence.active{border-left:4px solid var(--accent);background:color-mix(in srgb, var(--accent) 10%, var(--card))}
.en{font-weight:700;font-size:18px}
.cn{font-size:13px;color:var(--muted);margin-top:4px}
.lang-en .cn{display:none}
.lang-cn .en{display:none}

/* Audio */
.player{display:flex; align-items:center; gap:8px; margin:6px auto 10px; padding:0; background:transparent; border:none; box-shadow:none;}
.player audio{display:block; flex:1; width:100%; max-width:780px; height:34px; accent-color: var(--accent); background: transparent;}

/* Lesson bottom navigation */
.lesson-nav{display:flex; justify-content:space-between; gap:10px; padding:6px 0 16px; max-width:780px; margin:0 auto}
.btn-nav{display:inline-flex; align-items:center; justify-content:center; padding:8px 14px; min-width:96px;
  border-radius:999px; border:1px solid var(--border); background:var(--surface); color:inherit; text-decoration:none; box-shadow:var(--shadow);
  transition:transform .15s ease, box-shadow .15s ease}
.btn-nav:hover{transform:translateY(-2px); box-shadow:var(--shadow)}

/* Footer */
footer{padding:20px 0;color:var(--muted);text-align:center}
footer p{margin:4px 0; text-align:center}
.repo{margin-bottom:4px}

/* Links */
a{color:inherit}
a{text-decoration:none}

/* GitHub icon link */
.gh-link svg{width:18px;height:18px;fill:currentColor;opacity:.8;vertical-align:middle;transition:opacity .2s ease, transform .2s ease}
.gh-link:hover svg{opacity:1;transform:translateY(-1px)}

/* Smooth theme transitions for surfaces */
body, .card, .lesson-item, .sentence{ transition: background-color .35s ease, color .35s ease, box-shadow .35s ease, border-color .35s ease; }