/* NCE Learning Site */
:root {
  --primary: #4f46e5; --primary-hover: #4338ca; --primary-light: #eef2ff;
  --accent: #f59e0b; --accent-light: #fffbeb;
  --text: #1e293b; --text-secondary: #64748b; --text-muted: #94a3b8;
  --bg: #f8fafc; --white: #fff; --border: #e2e8f0; --border-light: #f1f5f9;
  --shadow: 0 1px 3px rgba(0,0,0,0.08); --header-h: 56px;
  font-family: -apple-system,BlinkMacSystemFont,"Segoe UI","Noto Sans SC",Roboto,sans-serif;
}
*,*::before,*::after{box-sizing:border-box;margin:0;padding:0}
body{color:var(--text);background:var(--bg);line-height:1.6;min-height:100vh}
a{color:var(--primary);text-decoration:none}
a:hover{text-decoration:underline}
.site-header{position:sticky;top:0;z-index:100;background:var(--white);border-bottom:1px solid var(--border);height:var(--header-h);display:flex;align-items:center;padding:0 20px;box-shadow:var(--shadow)}
.site-header .logo{font-weight:700;font-size:1.1rem;color:var(--primary);display:flex;align-items:center;gap:8px}
.site-header .logo span{color:var(--accent)}
.header-nav{margin-left:auto;display:flex;gap:12px}
.header-nav a{font-size:0.875rem;color:var(--text-secondary);padding:6px 12px;border-radius:6px}
.header-nav a:hover{background:var(--border-light);text-decoration:none}
.topbar{display:flex;align-items:center;gap:8px;padding:8px 16px;background:var(--white);border-bottom:1px solid var(--border);flex-wrap:wrap}
.topbar .back{font-size:0.85rem;color:var(--text-secondary);padding:4px 8px;border-radius:4px;white-space:nowrap}
.topbar .back:hover{background:var(--border-light);text-decoration:none}
.topbar .title-area{flex:1;min-width:0}
.topbar .lesson-num{font-size:0.75rem;font-weight:700;color:var(--text-muted)}
.topbar .lesson-title{font-size:0.9rem;font-weight:600;overflow:hidden;text-overflow:ellipsis;white-space:nowrap}
.play-btn{width:32px;height:32px;border-radius:50%;background:var(--primary);color:#fff;display:flex;align-items:center;justify-content:center;font-size:0.85rem;cursor:pointer;border:none;flex-shrink:0}
.play-btn:hover{background:var(--primary-hover)}
.play-btn.on{background:var(--accent)}
.audio-track{flex:1;height:6px;background:var(--border);border-radius:3px;cursor:pointer;min-width:60px;position:relative}
.audio-fill{height:100%;background:var(--primary);border-radius:3px;width:0%}
.audio-time{font-size:0.75rem;color:var(--text-muted);font-family:monospace;white-space:nowrap;min-width:36px}
.top-links{display:flex;gap:4px}
.nav-link{display:inline-block;padding:4px 10px;border-radius:6px;font-size:0.75rem;font-weight:600;background:var(--border-light);color:var(--text-secondary);white-space:nowrap}
.nav-link:hover{background:var(--border);text-decoration:none}
.nav-link.na{opacity:0.4;cursor:default}
.study-page{max-width:1400px;margin:0 auto;min-height:calc(100vh - var(--header-h));display:flex;flex-direction:column}
.study-main{flex:1;display:grid;grid-template-columns:1fr 1fr;min-height:0}
.study-left{padding:16px 20px;overflow-y:auto;border-right:1px solid var(--border);background:var(--white)}
.study-right{padding:16px 20px;overflow-y:auto;background:var(--bg)}
@media(max-width:768px){
  .study-main{grid-template-columns:1fr}
  .study-left{border-right:none;border-bottom:1px solid var(--border);max-height:50vh;overflow-y:auto}
  .study-right{max-height:none;overflow-y:visible}
  .topbar{padding:6px 10px}
  .topbar .lesson-title{font-size:0.8rem}
  .study-left,.study-right{padding:12px}
}
.sentence-list{display:flex;flex-direction:column;gap:2px}
.sentence-item{display:flex;align-items:flex-start;gap:10px;padding:10px 14px;border-radius:8px;border:2px solid transparent;transition:background 0.12s;color:var(--text);cursor:pointer}
.sentence-item:hover{background:var(--border-light);text-decoration:none}
.sentence-item:target,.sentence-item.s-target{background:var(--primary-light);border-color:var(--primary);font-weight:600}
.sentence-item .idx{font-size:0.75rem;color:var(--text-muted);min-width:24px;padding-top:1px;flex-shrink:0;text-align:center}
.sentence-item:target .idx,.sentence-item.s-target .idx{color:var(--primary);font-weight:700}
.sentence-item .text{font-size:1rem;line-height:1.5;flex:1;word-break:break-word}
/* Title item special styling */
.title-item{background:var(--accent-light);border-color:var(--accent)}
.title-item .text .en-title{font-weight:700;font-size:1.05rem}
.info-section{margin-bottom:20px}
.section-title{font-size:0.8rem;font-weight:700;color:var(--text-secondary);text-transform:uppercase;letter-spacing:0.05em;margin-bottom:8px;display:flex;align-items:center;gap:6px}
.chinese-block{font-size:1rem;line-height:1.8;padding:12px 16px;background:var(--accent-light);border-radius:8px;border-left:3px solid var(--accent);white-space:pre-wrap}
.vocab-grid{display:flex;flex-wrap:wrap;gap:4px}
.vocab-grid .word-item{background:var(--white);border-radius:4px;padding:6px 10px;border:1px solid var(--border-light);display:inline-flex;gap:4px;align-items:baseline}
.vocab-grid .word-item .en{font-weight:600;font-size:0.85rem}
.vocab-grid .word-item .pos{font-size:0.7rem;color:var(--text-muted)}
.vocab-grid .word-item .cn{font-size:0.8rem;color:var(--text-secondary)}
.notes-content{padding:12px 16px;background:var(--white);border-radius:8px;border:1px solid var(--border);font-size:0.9rem;line-height:1.7}
.note-title{font-weight:700;margin:10px 0 4px}
.note-line{margin-bottom:4px;padding-left:8px;border-left:2px solid var(--border-light)}
.bottombar{display:flex;align-items:center;justify-content:space-between;padding:10px 20px;background:var(--white);border-top:1px solid var(--border);gap:10px}
.bottombar .right{display:flex;gap:8px}
.btn-link,.btn-primary{padding:8px 16px;border-radius:8px;font-size:0.85rem;font-weight:600;display:inline-block}
.btn-link{background:var(--border-light);color:var(--text-secondary)}
.btn-link:hover{background:var(--border);text-decoration:none}
.btn-primary{background:var(--primary);color:#fff}
.btn-primary:hover{background:var(--primary-hover);text-decoration:none}