:root {
            --bg-color: #6a67ce;
            --card-bg: #ffffff;
            --text-main: #1f2937;
            --text-sub: #6b7280;
            --border-dashed: #cbd5e1;
            --upload-bg: #f9fafb;
            --btn-gradient: linear-gradient(90deg, #6366f1 0%, #db2777 100%);
            --btn-download: linear-gradient(135deg, #10b981 0%, #059669 100%);
            --icon-color: #6b7280;
            --primary: #6366f1;
            --danger: #ef4444;
        }

        body {
            font-family: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
            background-color: var(--bg-color);
            min-height: 100vh;
            display: flex;
            justify-content: center;
            align-items: center;
            margin: 0;
            padding: 20px;
            color: var(--text-main);
        }

        .container {
            background: var(--card-bg);
            width: 100%;
            max-width: 700px;
            border-radius: 20px;
            box-shadow: 0 20px 40px rgba(0, 0, 0, 0.2);
            padding: 2.5rem;
            display: flex;
            flex-direction: column;
            gap: 1.2rem;
        }

        header { text-align: center; margin-bottom: 5px; }
        h1 { 
            margin: 0; font-size: 1.8rem; font-weight: 700; color: #7c3aed;
            display: flex; align-items: center; justify-content: center; gap: 10px;
        }
        .subtitle { color: var(--text-sub); margin-top: 8px; font-size: 0.9rem; }

        .upload-area {
            border: 2px dashed var(--border-dashed);
            border-radius: 12px;
            padding: 2.5rem 1rem;
            text-align: center;
            cursor: pointer;
            background-color: var(--upload-bg);
            transition: all 0.3s ease;
            position: relative;
            overflow: hidden;
        }
        .upload-area:hover, .upload-area.drag-over {
            border-color: #6366f1; background-color: #f5f3ff;
        }
        .upload-icon { 
            font-size: 2.5rem; color: #6366f1; margin-bottom: 10px; 
            background: #fff; width: 50px; height: 50px; line-height: 50px;
            border-radius: 50%; display: inline-block;
            box-shadow: 0 4px 10px rgba(0,0,0,0.05);
            position: relative; z-index: 1;
        }
        .upload-text-main { font-weight: 600; font-size: 1rem; color: #374151; position: relative; z-index: 1;}
        .upload-area input { 
            position: absolute; top: 0; left: 0; width: 100%; height: 100%; 
            opacity: 0; cursor: pointer; z-index: 10; 
        }

        .toolbar {
            display: flex; justify-content: space-between; align-items: center;
            padding: 5px 10px; background: #f8fafc; border-radius: 8px;
            border: 1px solid #e2e8f0;
        }
        .toolbar-group { display: flex; align-items: center; gap: 10px; }
        .toolbar-label { font-size: 0.85rem; font-weight: 600; color: #64748b; }
        
        select.quality-select {
            padding: 4px 8px; border-radius: 6px; border: 1px solid #cbd5e1;
            font-size: 0.85rem; outline: none; color: #334155;
        }
        
        .tool-btn {
            background: white; border: 1px solid #cbd5e1; border-radius: 6px;
            padding: 4px 8px; font-size: 0.85rem; color: #64748b; cursor: pointer;
            transition: all 0.2s; display: flex; align-items: center; gap: 4px;
        }
        .tool-btn:hover { border-color: var(--primary); color: var(--primary); }
        .btn-clear:hover { border-color: var(--danger); color: var(--danger); background-color: #fef2f2; }

        .file-list {
            list-style: none; padding: 0; margin: 0;
            max-height: 280px; overflow-y: auto;
        }
        .file-list::-webkit-scrollbar { width: 4px; }
        .file-list::-webkit-scrollbar-thumb { background-color: #e5e7eb; border-radius: 2px; }

        .file-item {
            display: flex; align-items: center; padding: 12px 10px;
            border-bottom: 1px solid #f3f4f6; transition: background 0.2s; gap: 12px;
        }
        .file-item:last-child { border-bottom: none; }
        .file-item:hover { background-color: #f9fafb; }
        .file-item.drag-over-up { border-top: 2px solid #6366f1; }
        .file-item.drag-over-down { border-bottom: 2px solid #6366f1; }

        .file-info { flex: 1; min-width: 0; display: flex; flex-direction: column; }
        .file-name { font-weight: 500; font-size: 0.95rem; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
        .file-size { font-size: 0.75rem; color: #9ca3af; }

        .btn-icon {
            background: none; border: none; cursor: pointer; color: var(--icon-color);
            padding: 6px; transition: color 0.2s; font-size: 0.9rem;
        }
        .btn-icon:hover { color: #6366f1; }
        .btn-icon.delete:hover { color: #ef4444; }

        .merge-btn {
            background: var(--btn-gradient); color: white; border: none; padding: 1rem;
            border-radius: 12px; font-size: 1rem; font-weight: 600;
            cursor: pointer; width: 100%; transition: all 0.3s;
            display: flex; justify-content: center; align-items: center; gap: 8px;
            box-shadow: 0 4px 15px rgba(219, 39, 119, 0.2);
        }
        .merge-btn:hover:not(:disabled) { transform: translateY(-1px); opacity: 0.95; }
        .merge-btn:disabled { background: #e5e7eb; color: #9ca3af; cursor: not-allowed; box-shadow: none; }

        .progress-box { display: none; margin-top: 15px; }
        .progress-header { display: flex; justify-content: space-between; margin-bottom: 5px; font-size: 0.85rem; color: #475569; }
        .progress-bar-bg { background: #f1f5f9; height: 10px; border-radius: 5px; overflow: hidden; }
        .progress-bar-fill {
            background: var(--btn-gradient); height: 100%; width: 0%; transition: width 0.2s linear;
        }
        .time-text { text-align: right; font-size: 0.8rem; color: #94a3b8; margin-top: 5px; font-variant-numeric: tabular-nums; }

        .result-area {
            display: none; background: #f0fdf4; border: 1px solid #bbf7d0;
            padding: 1.5rem; border-radius: 16px; text-align: center; margin-top: 15px;
            animation: fadeIn 0.5s ease;
        }
        @keyframes fadeIn { from { opacity: 0; transform: translateY(10px); } to { opacity: 1; transform: translateY(0); } }

        .result-title { color: #15803d; font-weight: 700; font-size: 1.1rem; margin-bottom: 5px; }
        .result-meta { font-size: 0.85rem; color: #64748b; margin-bottom: 15px; }
        audio { width: 100%; margin-bottom: 20px; outline: none; border-radius: 30px; }
        .result-actions { display: flex; justify-content: center; gap: 15px; align-items: center; }
        .btn-download {
            background: var(--btn-download); color: white; text-decoration: none;
            padding: 10px 24px; border-radius: 50px; font-weight: 600; display: inline-flex; align-items: center; gap: 8px;
            box-shadow: 0 4px 12px rgba(16, 185, 129, 0.3); transition: all 0.2s;
        }
        .btn-download:hover { transform: translateY(-2px); box-shadow: 0 6px 15px rgba(16, 185, 129, 0.4); }
        .btn-secondary {
            background: transparent; border: 2px solid #e2e8f0; color: #64748b; padding: 8px 20px; border-radius: 50px;
            font-weight: 600; cursor: pointer; transition: all 0.2s;
        }
        .btn-secondary:hover { border-color: var(--primary); color: var(--primary); background: #f5f3ff; }