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

:root {
    --primary-color: #4a90e2;
    --secondary-color: #50c878;
    --bg-color: #f5f5f5;
    --card-bg: #ffffff;
    --text-color: #333333;
    --border-color: #e0e0e0;
    --shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
    --shadow-hover: 0 4px 16px rgba(0, 0, 0, 0.15);
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    background: var(--bg-color);
    color: var(--text-color);
    line-height: 1.6;
    direction: ltr;
}

body[dir="rtl"] {
    direction: rtl;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 20px;
}

header {
    background: var(--card-bg);
    padding: 20px;
    border-radius: 12px;
    box-shadow: var(--shadow);
    margin-bottom: 30px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: 15px;
}

h1 {
    font-size: 28px;
    color: var(--primary-color);
    font-weight: 600;
}

.language-selector select {
    padding: 10px 15px;
    border: 2px solid var(--border-color);
    border-radius: 8px;
    font-size: 16px;
    background: var(--card-bg);
    color: var(--text-color);
    cursor: pointer;
    transition: border-color 0.3s;
}

.language-selector select:hover {
    border-color: var(--primary-color);
}

.language-selector select:focus {
    outline: none;
    border-color: var(--primary-color);
}

.tabs {
    display: flex;
    gap: 10px;
    margin-bottom: 20px;
    background: var(--card-bg);
    padding: 10px;
    border-radius: 12px;
    box-shadow: var(--shadow);
}

.tab-btn {
    flex: 1;
    padding: 15px 20px;
    border: none;
    background: transparent;
    color: var(--text-color);
    font-size: 16px;
    font-weight: 500;
    cursor: pointer;
    border-radius: 8px;
    transition: all 0.3s;
}

.tab-btn:hover {
    background: var(--bg-color);
}

.tab-btn.active {
    background: var(--primary-color);
    color: white;
}

.section {
    display: none;
}

.section.active {
    display: block;
}

.upload-area {
    background: var(--card-bg);
    border: 3px dashed var(--border-color);
    border-radius: 12px;
    padding: 60px 20px;
    text-align: center;
    cursor: pointer;
    transition: all 0.3s;
    margin-bottom: 20px;
    box-shadow: var(--shadow);
}

.upload-area:hover {
    border-color: var(--primary-color);
    background: #fafafa;
}

.upload-content {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 15px;
}

.upload-content svg {
    color: var(--primary-color);
}

.upload-content p {
    font-size: 18px;
    color: var(--text-color);
}

.preview-container {
    background: var(--card-bg);
    padding: 20px;
    border-radius: 12px;
    box-shadow: var(--shadow);
    margin-bottom: 20px;
}

.preview-container video {
    width: 100%;
    max-width: 100%;
    border-radius: 8px;
    margin-bottom: 20px;
    background: #000;
}

.controls {
    display: flex;
    flex-direction: column;
    gap: 15px;
}

.time-display {
    text-align: center;
    font-size: 20px;
    font-weight: 600;
    color: var(--primary-color);
    padding: 10px;
    background: var(--bg-color);
    border-radius: 8px;
}

.range-controls {
    display: flex;
    align-items: center;
    gap: 15px;
    flex-wrap: wrap;
}

.range-controls label {
    min-width: 120px;
    font-weight: 500;
}

.range-controls input[type="range"] {
    flex: 1;
    min-width: 200px;
    height: 8px;
    border-radius: 4px;
    background: var(--bg-color);
    outline: none;
    -webkit-appearance: none;
}

.range-controls input[type="range"]::-webkit-slider-thumb {
    -webkit-appearance: none;
    appearance: none;
    width: 20px;
    height: 20px;
    border-radius: 50%;
    background: var(--primary-color);
    cursor: pointer;
}

.range-controls input[type="range"]::-moz-range-thumb {
    width: 20px;
    height: 20px;
    border-radius: 50%;
    background: var(--primary-color);
    cursor: pointer;
    border: none;
}

.range-controls input[type="number"] {
    width: 100px;
    padding: 8px;
    border: 2px solid var(--border-color);
    border-radius: 8px;
    font-size: 16px;
}

.process-btn {
    padding: 15px 30px;
    background: var(--primary-color);
    color: white;
    border: none;
    border-radius: 8px;
    font-size: 18px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s;
    box-shadow: var(--shadow);
}

.process-btn:hover {
    background: #357abd;
    transform: translateY(-2px);
    box-shadow: var(--shadow-hover);
}

.process-btn:active {
    transform: translateY(0);
}

.result-container {
    background: var(--card-bg);
    padding: 20px;
    border-radius: 12px;
    box-shadow: var(--shadow);
    text-align: center;
}

.result-container video {
    width: 100%;
    max-width: 100%;
    border-radius: 8px;
    margin-bottom: 20px;
    background: #000;
}

.download-btn {
    display: inline-block;
    padding: 15px 30px;
    background: var(--secondary-color);
    color: white;
    text-decoration: none;
    border-radius: 8px;
    font-size: 18px;
    font-weight: 600;
    transition: all 0.3s;
    box-shadow: var(--shadow);
}

.download-btn:hover {
    background: #45b869;
    transform: translateY(-2px);
    box-shadow: var(--shadow-hover);
}

.merge-upload-area {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 20px;
    margin-bottom: 20px;
}

.upload-slot {
    position: relative;
    background: var(--card-bg);
    border: 3px dashed var(--border-color);
    border-radius: 12px;
    padding: 30px 20px;
    text-align: center;
    cursor: pointer;
    transition: all 0.3s;
    box-shadow: var(--shadow);
    min-height: 200px;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
}

.upload-slot:hover {
    border-color: var(--primary-color);
    background: #fafafa;
}

.upload-slot .upload-content {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 10px;
}

.upload-slot .upload-content svg {
    color: var(--primary-color);
}

.merge-preview {
    width: 100%;
    max-width: 100%;
    border-radius: 8px;
    background: #000;
    margin-top: 10px;
}

.remove-video {
    position: absolute;
    top: 10px;
    right: 10px;
    width: 30px;
    height: 30px;
    border-radius: 50%;
    background: #ff4444;
    color: white;
    border: none;
    font-size: 20px;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.3s;
}

.remove-video:hover {
    background: #cc0000;
    transform: scale(1.1);
}

.merge-controls {
    text-align: center;
    margin-bottom: 20px;
}

.loading {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(0, 0, 0, 0.7);
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    z-index: 1000;
    color: white;
}

.loading.hidden {
    display: none;
}

.spinner {
    width: 50px;
    height: 50px;
    border: 5px solid rgba(255, 255, 255, 0.3);
    border-top-color: white;
    border-radius: 50%;
    animation: spin 1s linear infinite;
    margin-bottom: 20px;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

.hidden {
    display: none !important;
}

/* 响应式设计 */
@media (max-width: 768px) {
    .container {
        padding: 10px;
    }

    header {
        flex-direction: column;
        text-align: center;
    }

    h1 {
        font-size: 24px;
    }

    .tabs {
        flex-direction: column;
    }

    .upload-area {
        padding: 40px 15px;
    }

    .upload-content p {
        font-size: 16px;
    }

    .range-controls {
        flex-direction: column;
        align-items: stretch;
    }

    .range-controls label {
        min-width: auto;
    }

    .range-controls input[type="range"] {
        min-width: auto;
        width: 100%;
    }

    .range-controls input[type="number"] {
        width: 100%;
    }

    .merge-upload-area {
        grid-template-columns: 1fr;
    }

    .upload-slot {
        min-height: 150px;
        padding: 20px 15px;
    }

    .process-btn, .download-btn {
        width: 100%;
        padding: 12px 20px;
        font-size: 16px;
    }
}

@media (max-width: 480px) {
    h1 {
        font-size: 20px;
    }

    .upload-area {
        padding: 30px 10px;
    }

    .preview-container, .result-container {
        padding: 15px;
    }

    .time-display {
        font-size: 18px;
    }
}

/* RTL 支持 */
body[dir="rtl"] .remove-video {
    right: auto;
    left: 10px;
}

body[dir="rtl"] .range-controls {
    flex-direction: row-reverse;
}