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

        :root {
            --primary: #66BCB4;
            --dark: #0e0e0e;
            --bg: #f9faf5;
            --white: #ffffff;
            --border: #e0e0e0;
            --muted: #888;
            --red: #e74c3c;
        }

        body {
            font-family: 'Inter', 'Helvetica Neue', 'Segoe UI', sans-serif;
            background: var(--bg);
            color: var(--dark);
            min-height: 100vh;
        }

        /* NAV */
        nav {
            display: flex;
            align-items: center;
            padding: 0 40px;
            height: 64px;
            background: white;
            border-bottom: 1px solid var(--border);
            position: sticky;
            top: 0;
            z-index: 50;
        }

        .logo {
            font-size: 22px;
            font-weight: 700;
            text-decoration: none;
            color: var(--primary);
        }

        .nav-back {
            display: flex;
            align-items: center;
            gap: 8px;
            margin-left: 24px;
            color: var(--muted);
            font-size: 13px;
            text-decoration: none;
            transition: color 0.15s;
        }
        .nav-back:hover { color: var(--dark); }

        .nav-right {
            margin-left: auto;
            display: flex;
            align-items: center;
            gap: 12px;
        }

        .btn-login {
            background: none;
            border: 1px solid var(--border);
            padding: 8px 18px;
            border-radius: 100px;
            font-size: 13px;
            cursor: pointer;
            font-family: inherit;
        }

        .btn-start {
            background: var(--dark);
            color: white;
            border: none;
            padding: 9px 20px;
            border-radius: 100px;
            font-size: 13px;
            font-weight: 500;
            cursor: pointer;
            font-family: inherit;
        }

        /* HERO */
        .tool-hero {
            text-align: center;
            padding: 60px 40px 40px;
        }

        .tool-icon-big {
            width: 72px;
            height: 72px;
            background: #f0fff8;
            border-radius: 20px;
            display: flex;
            align-items: center;
            justify-content: center;
            margin: 0 auto 20px;
            font-size: 32px;
        }

        .tool-hero h1 {
            font-size: 36px;
            font-weight: 700;
            letter-spacing: -1px;
            margin-bottom: 10px;
        }

        .tool-hero p {
            font-size: 16px;
            color: var(--muted);
            max-width: 480px;
            margin: 0 auto;
        }

        /* MAIN AREA */
        .tool-area {
            max-width: 800px;
            margin: 0 auto;
            padding: 0 40px 80px;
        }

        /* DROP ZONE */
        .drop-zone {
            border: 2px dashed var(--border);
            border-radius: 20px;
            padding: 60px 40px;
            text-align: center;
            cursor: pointer;
            transition: all 0.2s;
            background: white;
            margin-bottom: 24px;
        }

        .drop-zone:hover, .drop-zone.dragover {
            border-color: var(--primary);
            background: #f0fffc;
        }

        .drop-zone-icon {
            font-size: 40px;
            color: var(--primary);
            margin-bottom: 16px;
        }

        .drop-zone h3 {
            font-size: 18px;
            font-weight: 600;
            margin-bottom: 8px;
        }

        .drop-zone p {
            font-size: 13px;
            color: var(--muted);
            margin-bottom: 20px;
        }

        .btn-select {
            background: var(--primary);
            color: white;
            border: none;
            padding: 12px 28px;
            border-radius: 100px;
            font-size: 14px;
            font-weight: 600;
            cursor: pointer;
            font-family: inherit;
            transition: opacity 0.15s;
        }
        .btn-select:hover { opacity: 0.85; }

        #fileInput { display: none; }

        /* FILES PANEL */
        .files-panel {
            display: none;
            background: white;
            border: 1px solid var(--border);
            border-radius: 16px;
            padding: 24px;
            margin-bottom: 24px;
        }
        .files-panel.visible { display: block; }

        .panel-header {
            display: flex;
            align-items: center;
            justify-content: space-between;
            margin-bottom: 16px;
        }

        .panel-title {
            font-size: 14px;
            font-weight: 600;
        }

        .panel-count {
            font-size: 12px;
            color: var(--muted);
            background: var(--bg);
            padding: 3px 10px;
            border-radius: 100px;
        }

        /* FILE LIST */
        .file-list {
            display: flex;
            flex-direction: column;
            gap: 8px;
            margin-bottom: 16px;
        }

        .file-item {
            display: flex;
            align-items: center;
            gap: 12px;
            padding: 10px 12px;
            background: var(--bg);
            border-radius: 10px;
            border: 1px solid var(--border);
            transition: border-color 0.15s;
            cursor: grab;
            user-select: none;
        }
        .file-item:active { cursor: grabbing; }
        .file-item.dragging { opacity: 0.4; }
        .file-item.drag-over { border-color: var(--primary); background: #f0fffc; }

        .file-num {
            width: 22px;
            height: 22px;
            background: var(--primary);
            color: white;
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
            font-size: 11px;
            font-weight: 700;
            flex-shrink: 0;
        }

        .drag-handle {
            color: #ccc;
            font-size: 14px;
            cursor: grab;
            flex-shrink: 0;
        }

        .file-icon {
            width: 38px;
            height: 38px;
            background: #fff0f0;
            border-radius: 8px;
            display: flex;
            align-items: center;
            justify-content: center;
            font-size: 18px;
            flex-shrink: 0;
        }

        .file-details { flex: 1; min-width: 0; }
        .file-name {
            font-size: 13px;
            font-weight: 600;
            white-space: nowrap;
            overflow: hidden;
            text-overflow: ellipsis;
        }
        .file-size { font-size: 11px; color: var(--muted); }

        .file-actions { display: flex; gap: 6px; flex-shrink: 0; }

        .btn-mv, .btn-del {
            background: none;
            border: 1px solid var(--border);
            width: 28px;
            height: 28px;
            border-radius: 7px;
            cursor: pointer;
            color: var(--muted);
            font-size: 11px;
            display: flex;
            align-items: center;
            justify-content: center;
            transition: all 0.15s;
        }
        .btn-mv:hover { background: var(--bg); border-color: #ccc; color: var(--dark); }
        .btn-del:hover { background: #fff0f0; border-color: var(--red); color: var(--red); }

        /* ADD MORE */
        .btn-add-more {
            width: 100%;
            background: none;
            border: 1.5px dashed var(--border);
            border-radius: 10px;
            padding: 10px;
            font-size: 13px;
            color: var(--muted);
            cursor: pointer;
            font-family: inherit;
            font-weight: 500;
            transition: all 0.15s;
        }
        .btn-add-more:hover { border-color: var(--primary); color: var(--primary); }

        /* OPTIONS */
        .merge-options {
            margin-top: 20px;
            padding-top: 20px;
            border-top: 1px solid var(--border);
        }

        .options-title {
            font-size: 13px;
            font-weight: 600;
            margin-bottom: 12px;
        }

        .option-row {
            display: flex;
            align-items: center;
            justify-content: space-between;
            padding: 10px 0;
            border-bottom: 1px solid #f0f0f0;
        }
        .option-row:last-child { border-bottom: none; }

        .option-text .option-label { font-size: 13px; font-weight: 500; }
        .option-text .option-hint { font-size: 11px; color: var(--muted); margin-top: 2px; }

        .toggle {
            width: 40px;
            height: 22px;
            background: var(--border);
            border-radius: 100px;
            position: relative;
            cursor: pointer;
            flex-shrink: 0;
            transition: background 0.2s;
        }
        .toggle.on { background: var(--primary); }
        .toggle::after {
            content: '';
            position: absolute;
            top: 3px;
            left: 3px;
            width: 16px;
            height: 16px;
            background: white;
            border-radius: 50%;
            transition: left 0.2s;
        }
        .toggle.on::after { left: 21px; }

        /* MERGE BTN */
        .btn-merge {
            width: 100%;
            background: var(--primary);
            color: white;
            border: none;
            padding: 16px;
            border-radius: 12px;
            font-size: 15px;
            font-weight: 600;
            cursor: pointer;
            font-family: inherit;
            transition: opacity 0.15s;
            display: flex;
            align-items: center;
            justify-content: center;
            gap: 10px;
            margin-top: 20px;
        }
        .btn-merge:hover { opacity: 0.85; }
        .btn-merge:disabled { opacity: 0.5; cursor: not-allowed; }

        /* PROGRESS */
        .progress-area {
            display: none;
            background: white;
            border: 1px solid var(--border);
            border-radius: 16px;
            padding: 24px;
            margin-bottom: 24px;
            text-align: center;
        }
        .progress-area.visible { display: block; }

        .progress-bar-wrap {
            background: #f0f0f0;
            border-radius: 100px;
            height: 8px;
            overflow: hidden;
            margin-bottom: 10px;
        }
        .progress-bar {
            height: 100%;
            background: var(--primary);
            border-radius: 100px;
            width: 0%;
            transition: width 0.3s ease;
        }
        .progress-label { font-size: 13px; color: var(--muted); }

        /* RESULT */
        .result-area {
            display: none;
            background: white;
            border: 1px solid var(--border);
            border-radius: 16px;
            padding: 24px;
            margin-bottom: 24px;
        }
        .result-area.visible { display: block; }

        .result-success {
            display: flex;
            align-items: center;
            gap: 16px;
            margin-bottom: 20px;
            padding: 16px;
            background: #f0fff8;
            border-radius: 12px;
            border: 1px solid #b7e4d4;
        }
        .result-success-icon {
            width: 44px;
            height: 44px;
            background: var(--primary);
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
            color: white;
            font-size: 18px;
            flex-shrink: 0;
        }
        .result-success-title { font-size: 15px; font-weight: 600; margin-bottom: 2px; }
        .result-success-sub { font-size: 13px; color: var(--muted); }

        .result-stats {
            display: grid;
            grid-template-columns: repeat(3, 1fr);
            gap: 12px;
            margin-bottom: 20px;
        }
        .stat-box {
            text-align: center;
            padding: 14px;
            border-radius: 12px;
            background: var(--bg);
        }
        .stat-box-label { font-size: 11px; color: var(--muted); margin-bottom: 4px; text-transform: uppercase; letter-spacing: 0.5px; }
        .stat-box-value { font-size: 20px; font-weight: 700; }
        .stat-box-value.green { color: #16a34a; }

        .result-actions { display: flex; gap: 10px; }

        .btn-download {
            flex: 1;
            background: var(--dark);
            color: white;
            border: none;
            padding: 14px;
            border-radius: 12px;
            font-size: 14px;
            font-weight: 600;
            cursor: pointer;
            font-family: inherit;
            transition: opacity 0.15s;
            display: flex;
            align-items: center;
            justify-content: center;
            gap: 8px;
        }
        .btn-download:hover { opacity: 0.85; }

        .btn-again {
            background: none;
            border: 1px solid var(--border);
            padding: 14px 20px;
            border-radius: 12px;
            font-size: 14px;
            cursor: pointer;
            font-family: inherit;
            transition: background 0.15s;
        }
        .btn-again:hover { background: var(--bg); }

        /* PRIVACY BADGE */
        .privacy-badge {
            display: flex;
            align-items: center;
            justify-content: center;
            gap: 8px;
            font-size: 12px;
            color: var(--muted);
            margin-top: 14px;
        }
        .privacy-badge i { color: var(--primary); }

        /* ERROR */
        .error-msg {
            display: none;
            background: #fff0f0;
            border: 1px solid #fcc;
            border-radius: 12px;
            padding: 14px 18px;
            font-size: 13px;
            color: var(--red);
            margin-bottom: 16px;
            text-align: center;
        }
        .error-msg.visible { display: block; }

        /* HOW IT WORKS */
        .how-section {
            max-width: 800px;
            margin: 0 auto;
            padding: 0 40px 80px;
        }
        .how-section h2 {
            font-size: 22px;
            font-weight: 700;
            margin-bottom: 20px;
            text-align: center;
        }
        .steps {
            display: grid;
            grid-template-columns: repeat(3, 1fr);
            gap: 16px;
        }
        .step {
            background: white;
            border: 1px solid var(--border);
            border-radius: 14px;
            padding: 20px;
            text-align: center;
        }
        .step-num {
            width: 32px;
            height: 32px;
            background: var(--primary);
            color: white;
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
            font-size: 13px;
            font-weight: 700;
            margin: 0 auto 10px;
        }
        .step-title { font-size: 14px; font-weight: 600; margin-bottom: 4px; }
        .step-desc { font-size: 12px; color: var(--muted); line-height: 1.5; }