:root{
      --bg1:#f7fbff;
      --bg2:#eef6ff;

      --card:#ffffff;
      --text:#0f172a;
      --muted:#475569;

      --blue:#2563eb;
      --blue2:#38bdf8;

      --border: rgba(15, 23, 42, 0.10);
      --shadow: 0 10px 18px -8px rgba(2, 8, 23, 0.18);
      --radius: 14px;
      --transition: all .25s ease;
    }

    *{margin:0;padding:0;box-sizing:border-box}

    body{
      font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
      background: linear-gradient(135deg, var(--bg1) 0%, var(--bg2) 100%);
      color: var(--text);
      line-height: 1.6;
      min-height: 100vh;
      padding: 20px;
    }

    .container{max-width:1000px;margin:0 auto;padding:0 20px}

    .header{
      background: linear-gradient(135deg, rgba(37,99,235,.10) 0%, rgba(56,189,248,.12) 100%);
      border: 1px solid var(--border);
      border-radius: var(--radius);
      padding: 28px;
      margin-bottom: 26px;
      box-shadow: var(--shadow);
      position: relative;
      overflow: hidden;
    }

    .header::before{
      content:"";
      position:absolute;
      top: -40px;
      right: -40px;
      width: 160px;
      height: 160px;
      background: radial-gradient(circle at center, rgba(56,189,248,.25), transparent 60%);
      border-radius: 50%;
    }

    .header h1{font-size:2.2rem;margin-bottom:8px;position:relative}
    .header .subtitle{color:var(--muted);margin-bottom:18px;position:relative}

    .nav-icons{
      display:flex;
      flex-wrap:wrap;
      gap:12px;
      position:relative;
    }

    .nav-btn{
      display:flex;
      align-items:center;
      gap:10px;
      padding:12px 18px;
      background:#fff;
      border:1px solid var(--border);
      border-radius: 10px;
      color: var(--text);
      text-decoration:none;
      font-weight: 600;
      transition: var(--transition);
      box-shadow: 0 6px 14px -10px rgba(2, 8, 23, 0.35);
    }

    .nav-btn:hover{transform:translateY(-2px);border-color:rgba(37,99,235,.35)}
    .nav-btn i{color:var(--blue)}

    .content{display:grid;grid-template-columns:1fr;gap:22px}
    @media (min-width:768px){
      .content{grid-template-columns:1fr 1fr}
      .audio-section{grid-column:1 / 3}
    }

    .section-card{
      background: var(--card);
      border: 1px solid var(--border);
      border-radius: var(--radius);
      padding: 22px;
      box-shadow: var(--shadow);
      transition: var(--transition);
    }
    .section-card:hover{transform:translateY(-2px)}

    .section-title{
      font-size: 1.35rem;
      margin-bottom: 16px;
      padding-bottom: 10px;
      border-bottom: 2px solid rgba(37,99,235,.22);
      display:flex;
      align-items:center;
      gap:10px;
    }
    .section-title i{color:var(--blue)}

    .audio-player{width:100%;margin-top:10px}
    .audio-player audio{width:100%;border-radius:10px}

    .audio-info{
      display:flex;
      justify-content:space-between;
      margin-top:12px;
      color: var(--muted);
      font-size:.92rem;
      gap:10px;
      flex-wrap: wrap;
    }

    .pdf-box{
      background: linear-gradient(135deg, rgba(37,99,235,.06) 0%, rgba(56,189,248,.08) 100%);
      border:1px solid rgba(37,99,235,.14);
      border-radius: var(--radius);
      padding: 22px;
      text-align:center;
      display:flex;
      flex-direction:column;
      align-items:center;
      justify-content:center;
      min-height: 180px;
    }
    .pdf-box p{margin-bottom:16px;color:var(--muted)}

    .pdf-btn{
      display:inline-flex;
      align-items:center;
      gap:10px;
      padding: 12px 22px;
      background: linear-gradient(135deg, var(--blue) 0%, var(--blue2) 100%);
      color:#fff;
      border-radius: 10px;
      text-decoration:none;
      font-weight: 700;
      transition: var(--transition);
      box-shadow: 0 10px 18px -12px rgba(37,99,235,.7);
    }
    .pdf-btn:hover{transform:translateY(-2px)}

    .vocab-list{list-style:none}
    .vocab-list li{
      padding: 12px 14px;
      margin-bottom: 10px;
      border:1px solid var(--border);
      border-radius: 12px;
      background: rgba(37,99,235,.03);
    }
    .vocab-list li strong{color:var(--blue)}

    .footer{
      text-align:center;
      margin-top: 34px;
      padding-top: 18px;
      border-top: 1px solid var(--border);
      color: var(--muted);
      font-size: .9rem;
    }

    @media (max-width:768px){
      .header h1{font-size:1.8rem;text-align:center}
      .subtitle{text-align:center}
      .nav-icons{justify-content:center}
      .nav-btn{flex:1;min-width:150px;justify-content:center}
    }
    @media (max-width:480px){
      .header{padding:20px}
      .nav-btn{min-width:100%}