:root {
    --primary-color: #667eea;
    --secondary-color: #764ba2;
    --success-color: #28a745;
    --error-color: #dc3545;
    --warning-color: #ffc107;
    --info-color: #17a2b8;
    --dark-color: #2c3e50;
}

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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    line-height: 1.6;
    background: linear-gradient(135deg, var(--primary-color) 0%, var(--secondary-color) 100%);
    min-height: 100vh;
    padding: 20px;
    padding-top: 60px;
}

/* Back Button */
.back-button {
    position: fixed;
    top: 10px;
    left: 20px;
    background: rgba(255, 255, 255, 0.95);
    color: #333;
    padding: 10px 20px;
    border-radius: 30px;
    text-decoration: none;
    font-weight: 600;
    font-size: 0.95rem;
    border: none;
    cursor: pointer;
    z-index: 1000;
    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
    transition: all 0.2s;
}

.back-button:hover {
    background: white;
    transform: translateX(-3px);
    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.15);
}

/* Breadcrumb */
.breadcrumb-nav {
    max-width: 1000px;
    margin: 0 auto;
    padding: 0 20px 10px;
}

.breadcrumb {
    list-style: none;
    display: flex;
    gap: 8px;
    font-size: 0.9rem;
    flex-wrap: wrap;
}

.breadcrumb li {
    display: flex;
    align-items: center;
    color: rgba(255, 255, 255, 0.9);
}

.breadcrumb li:not(:last-child)::after {
    content: '›';
    margin-left: 8px;
    color: rgba(255, 255, 255, 0.6);
    font-size: 1.2rem;
}

.breadcrumb a {
    color: white;
    text-decoration: none;
    transition: opacity 0.2s;
}

.breadcrumb a:hover {
    opacity: 0.8;
    text-decoration: underline;
}

.breadcrumb [aria-current="page"] {
    color: white;
    font-weight: 600;
}

/* Tool Switcher */
.tool-switcher {
    display: flex;
    align-items: center;
    gap: 8px;
    flex-wrap: wrap;
    background: rgba(255, 255, 255, 0.12);
    border: 1px solid rgba(255, 255, 255, 0.2);
    border-radius: 14px;
    padding: 10px 16px;
    margin: 0 auto 16px;
    max-width: 1000px;
}

.tool-switcher-label {
    color: rgba(255, 255, 255, 0.7);
    font-size: 0.8rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.5px;
    margin-right: 4px;
    white-space: nowrap;
}

.tool-switch-btn {
    color: rgba(255, 255, 255, 0.85);
    text-decoration: none;
    font-size: 0.85rem;
    font-weight: 500;
    padding: 6px 14px;
    border-radius: 20px;
    border: 1px solid rgba(255, 255, 255, 0.2);
    background: rgba(255, 255, 255, 0.1);
    transition: all 0.2s;
    white-space: nowrap;
    display: inline-block;
}

.tool-switch-btn:hover {
    background: rgba(255, 255, 255, 0.25);
    color: white;
}

.tool-switch-btn.active {
    background: white;
    color: #667eea;
    font-weight: 700;
    border-color: white;
    pointer-events: none;
}

/* Container */
.container {
    max-width: 1000px;
    margin: 0 auto 40px;
    background: white;
    border-radius: 15px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.2);
    overflow: hidden;
}

/* Header */
.header {
    background: var(--dark-color);
    color: white;
    padding: 25px;
    text-align: center;
}

.header h1 {
    font-size: 2rem;
    margin-bottom: 8px;
}

/* Main content */
.main-content {
    padding: 30px;
}

/* Upload Box */
.upload-box {
    border: 3px dashed var(--primary-color);
    border-radius: 10px;
    padding: 50px 20px;
    text-align: center;
    transition: all 0.2s;
    background: #f8f9fa;
    cursor: pointer;
    margin-bottom: 25px;
}

.upload-box:hover {
    border-color: var(--secondary-color);
    background: #e9ecef;
}

.upload-box.dragover {
    border-color: var(--success-color);
    background: #d4edda;
}

.upload-icon {
    font-size: 3rem;
    margin-bottom: 15px;
    color: var(--primary-color);
}

.browse-button {
    background: var(--primary-color);
    color: white;
    padding: 10px 25px;
    border: none;
    border-radius: 20px;
    font-size: 1rem;
    cursor: pointer;
    transition: all 0.2s;
    margin-top: 12px;
    font-weight: 600;
}

.browse-button:hover {
    background: var(--secondary-color);
    transform: translateY(-2px);
}

#fileInput {
    display: none;
}

/* Messages */
.message {
    padding: 12px;
    border-radius: 6px;
    margin-top: 15px;
    display: none;
    font-size: 0.9rem;
}

.message.show {
    display: block;
}

.error-message {
    background: #f8d7da;
    color: var(--error-color);
    border: 1px solid #f5c6cb;
}

.warning-message {
    background: #fff3cd;
    color: #856404;
    border: 1px solid #ffeaa7;
}

.info-message {
    background: #d1ecf1;
    color: #0c5460;
    border: 1px solid #bee5eb;
}

/* Files List */
.files-list {
    margin-bottom: 25px;
    display: none;
}

.files-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 15px;
    padding-bottom: 10px;
    border-bottom: 2px solid #e9ecef;
}

.files-count {
    font-weight: 600;
    color: var(--dark-color);
}

.clear-all {
    background: var(--error-color);
    color: white;
    border: none;
    padding: 6px 14px;
    border-radius: 15px;
    cursor: pointer;
    font-size: 0.82rem;
    font-weight: 600;
    transition: all 0.2s;
}

.clear-all:hover {
    background: #c82333;
    transform: translateY(-1px);
}

.file-item {
    display: flex;
    align-items: center;
    padding: 14px 16px;
    background: #f8f9fa;
    border-radius: 8px;
    margin-bottom: 10px;
    border: 2px solid transparent;
    transition: all 0.2s;
}

.file-item:hover {
    background: #e9ecef;
}

.file-item.dragging {
    opacity: 0.45;
    background: #dee2e6;
}

.file-item.over {
    border-color: var(--primary-color);
    background: #eef0ff;
}

.move-handle {
    cursor: grab;
    padding: 4px 8px;
    border-radius: 4px;
    color: #adb5bd;
    font-size: 1.1rem;
    margin-right: 8px;
    user-select: none;
}

.move-handle:hover {
    background: #dee2e6;
    color: var(--dark-color);
}

.file-order-badge {
    background: var(--primary-color);
    color: white;
    border-radius: 50%;
    width: 24px;
    height: 24px;
    font-size: 0.75rem;
    font-weight: 700;
    display: flex;
    align-items: center;
    justify-content: center;
    margin-right: 12px;
    flex-shrink: 0;
}

.file-icon {
    font-size: 1.4rem;
    margin-right: 12px;
    color: var(--error-color);
    flex-shrink: 0;
}

.file-details {
    flex: 1;
    min-width: 0;
}

.file-name {
    font-weight: 600;
    color: var(--dark-color);
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

.file-size {
    font-size: 0.8rem;
    color: #6c757d;
    margin-top: 2px;
}

.file-actions {
    display: flex;
    gap: 6px;
    margin-left: 12px;
    flex-shrink: 0;
}

.file-action {
    background: none;
    border: 1px solid #dee2e6;
    cursor: pointer;
    padding: 5px 9px;
    border-radius: 6px;
    transition: all 0.2s;
    color: #6c757d;
    font-size: 0.85rem;
}

.file-action:hover {
    background: #dee2e6;
    color: var(--dark-color);
    border-color: #adb5bd;
}

.file-action.remove:hover {
    background: #f8d7da;
    color: var(--error-color);
    border-color: #f5c6cb;
}

/* Controls Section */
.controls-section {
    background: #f8f9fa;
    border-radius: 10px;
    padding: 25px;
    margin-bottom: 25px;
    display: none;
}

.controls-section h3 {
    margin-bottom: 20px;
    color: var(--dark-color);
}

.controls-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
    gap: 20px;
}

.control-group {
    margin-bottom: 5px;
}

.control-label {
    display: block;
    margin-bottom: 8px;
    font-weight: 600;
    color: #333;
    font-size: 0.9rem;
}

.control-select,
.control-input {
    width: 100%;
    padding: 10px;
    border: 2px solid #e9ecef;
    border-radius: 8px;
    font-size: 0.9rem;
    transition: all 0.2s;
    background: white;
}

.control-select:focus,
.control-input:focus {
    border-color: var(--primary-color);
    outline: none;
}

.checkbox-group {
    display: flex;
    align-items: center;
    gap: 10px;
    margin-top: 4px;
}

.checkbox-group input {
    width: 18px;
    height: 18px;
    cursor: pointer;
}

.checkbox-group label {
    cursor: pointer;
    font-size: 0.9rem;
    color: #333;
}

/* Progress */
.progress-section {
    display: none;
    margin: 20px 0;
    text-align: center;
}

.progress-section.show {
    display: block;
}

.progress-bar {
    width: 100%;
    height: 8px;
    background: #e9ecef;
    border-radius: 4px;
    overflow: hidden;
    margin: 15px 0;
}

.progress-fill {
    height: 100%;
    background: var(--success-color);
    border-radius: 4px;
    transition: width 0.3s ease;
    width: 0%;
}

.progress-text {
    font-size: 0.9rem;
    color: #6c757d;
}

/* Result Section */
.result-section {
    display: none;
    margin: 20px 0;
    text-align: center;
    padding: 30px;
    background: #d4edda;
    border-radius: 10px;
    border: 2px solid #c3e6cb;
}

.result-section.show {
    display: block;
}

.result-icon {
    font-size: 3rem;
    margin-bottom: 12px;
}

/* Action Buttons */
.action-buttons {
    display: flex;
    gap: 15px;
    justify-content: center;
    margin-top: 25px;
    flex-wrap: wrap;
}

.action-button {
    color: white;
    padding: 14px 30px;
    border: none;
    border-radius: 25px;
    cursor: pointer;
    font-weight: 600;
    font-size: 1rem;
    transition: all 0.2s;
    display: inline-flex;
    align-items: center;
    gap: 8px;
}

.action-button:hover:not(:disabled) {
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
}

.action-button:disabled {
    background: #6c757d !important;
    cursor: not-allowed;
    transform: none;
    box-shadow: none;
}

.btn-merge {
    background: var(--success-color);
}

.btn-merge:hover:not(:disabled) {
    background: #218838;
}

.btn-reset {
    background: var(--warning-color);
    color: #333;
}

.btn-reset:hover:not(:disabled) {
    background: #e0a800;
}

.btn-download {
    background: var(--success-color);
    margin-top: 15px;
}

.btn-download:hover {
    background: #218838;
}

/* Features */
.features {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 20px;
    margin-top: 10px;
    padding: 30px;
    background: #f8f9fa;
    border-radius: 10px;
}

.feature {
    text-align: center;
    padding: 20px;
}

.feature-icon {
    font-size: 2.2rem;
    margin-bottom: 12px;
    color: var(--primary-color);
}

/* SEO Content */
.seo-content {
    padding: 30px;
    border-top: 1px solid #eee;
}

.seo-content h2 {
    font-size: 1.2rem;
    color: #2c3e50;
    margin: 20px 0 8px;
}

.seo-content h2:first-child {
    margin-top: 0;
}

.seo-content p {
    font-size: 0.95rem;
    color: #555;
    line-height: 1.7;
}

.seo-content ul {
    margin: 8px 0 14px 20px;
}

.seo-content ul li {
    margin-bottom: 6px;
    font-size: 0.95rem;
    color: #555;
}

/* FAQ */
.faq-section {
    padding: 30px;
    background: #f8f9fa;
    border-top: 1px solid #eee;
}

.faq-section h2 {
    text-align: center;
    margin-bottom: 24px;
    color: #333;
    font-size: 1.5rem;
}

.faq-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 16px;
}

.faq-item {
    background: white;
    padding: 15px 20px;
    border-radius: 8px;
    box-shadow: 0 2px 5px rgba(0, 0, 0, 0.05);
}

.faq-item summary {
    font-weight: 600;
    color: #333;
    cursor: pointer;
    padding: 5px 0;
}

.faq-item summary:hover {
    color: var(--primary-color);
}

.faq-item p {
    margin-top: 10px;
    color: #555;
    line-height: 1.6;
    font-size: 0.95rem;
}

/* Related Tools */
.related-tools {
    padding: 30px;
    text-align: center;
    border-top: 1px solid #eee;
}

.related-tools h2 {
    margin-bottom: 20px;
    color: #333;
    font-size: 1.4rem;
}

.related-links {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 12px;
}

.related-link {
    display: inline-block;
    padding: 10px 20px;
    background: #e9ecef;
    color: #333;
    text-decoration: none;
    border-radius: 25px;
    font-weight: 500;
    font-size: 0.9rem;
    transition: all 0.2s;
}

.related-link:hover {
    background: var(--primary-color);
    color: white;
    transform: translateY(-2px);
}

/* Footer */
footer {
    background: rgba(0, 0, 0, 0.3);
    color: rgba(255, 255, 255, 0.85);
    padding: 20px;
    text-align: center;
    font-size: 0.9rem;
    border-radius: 0 0 15px 15px;
}

footer a {
    color: white;
    text-decoration: none;
}

footer a:hover {
    text-decoration: underline;
}

/* Responsive */
@media (max-width: 768px) {
    body {
        padding-top: 55px;
    }

    .back-button {
        top: 8px;
        left: 10px;
        padding: 8px 16px;
        font-size: 0.85rem;
    }

    .main-content {
        padding: 20px;
    }

    .upload-box {
        padding: 30px 15px;
    }

    .action-buttons {
        flex-direction: column;
        align-items: stretch;
    }

    .action-button {
        justify-content: center;
    }

    .faq-grid {
        grid-template-columns: 1fr;
    }

    .related-links {
        flex-direction: column;
        align-items: stretch;
    }

    .related-link {
        text-align: center;
    }

    .file-item {
        flex-wrap: wrap;
        gap: 8px;
    }

    .file-actions {
        margin-left: auto;
    }
}

@media (max-width: 600px) {
    .tool-switcher {
        gap: 6px;
        padding: 8px 12px;
    }

    .tool-switch-btn {
        font-size: 0.78rem;
        padding: 5px 10px;
    }
}