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

:root {
    --color-primary: #2563eb;
    --color-primary-hover: #1d4ed8;
    --color-bg: #f8fafc;
    --color-card: #ffffff;
    --color-text: #1e293b;
    --color-text-muted: #64748b;
    --color-border: #e2e8f0;
    --color-border-hover: #cbd5e1;
    --color-success: #059669;
    --color-success-bg: #ecfdf5;
    --color-error: #dc2626;
    --color-error-bg: #fef2f2;
    --radius: 12px;
    --radius-sm: 8px;
    --shadow: 0 1px 3px rgba(0, 0, 0, 0.08), 0 4px 12px rgba(0, 0, 0, 0.04);
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    background: var(--color-bg);
    color: var(--color-text);
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 20px;
    line-height: 1.5;
}

.container {
    width: 100%;
    max-width: 480px;
}

.card {
    background: var(--color-card);
    border-radius: var(--radius);
    border: 1px solid var(--color-border);
    padding: 32px;
    box-shadow: var(--shadow);
}

/* Header */
.header {
    text-align: center;
    margin-bottom: 28px;
}

.logo {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 12px;
    margin-bottom: 16px;
    color: var(--color-primary);
}

.logo .arrow {
    color: var(--color-text-muted);
}

.header h1 {
    font-size: 24px;
    font-weight: 700;
    color: var(--color-text);
    margin-bottom: 4px;
}

.subtitle {
    color: var(--color-text-muted);
    font-size: 15px;
}

/* Alert messages */
.alert {
    display: flex;
    align-items: center;
    gap: 10px;
    padding: 12px 16px;
    border-radius: var(--radius-sm);
    margin-bottom: 20px;
    font-size: 14px;
    font-weight: 500;
}

.alert-error {
    background: var(--color-error-bg);
    color: var(--color-error);
    border: 1px solid #fecaca;
}

.alert-success {
    background: var(--color-success-bg);
    color: var(--color-success);
    border: 1px solid #a7f3d0;
}

/* Upload zone */
.upload-zone {
    border: 2px dashed var(--color-border);
    border-radius: var(--radius);
    padding: 40px 24px;
    text-align: center;
    cursor: pointer;
    transition: all 0.2s ease;
    position: relative;
    background: var(--color-bg);
    margin-bottom: 24px;
}

.upload-zone:hover {
    border-color: var(--color-border-hover);
    background: #f1f5f9;
}

.upload-zone.dragover {
    border-color: var(--color-primary);
    background: #eff6ff;
}

.upload-zone.has-file {
    border-color: var(--color-success);
    border-style: solid;
    background: var(--color-success-bg);
}

.upload-zone.has-file .upload-content {
    display: none;
}

.upload-zone.has-file .file-selected {
    display: flex;
}

.upload-zone input[type="file"] {
    position: absolute;
    inset: 0;
    opacity: 0;
    cursor: pointer;
}

.upload-icon {
    color: var(--color-text-muted);
    margin-bottom: 12px;
}

.upload-text {
    font-size: 16px;
    color: var(--color-text);
    margin-bottom: 4px;
}

.upload-hint {
    font-size: 14px;
    color: var(--color-text-muted);
}

.file-selected {
    display: none;
    align-items: center;
    justify-content: center;
    gap: 10px;
    color: var(--color-success);
    font-weight: 500;
}

/* Options */
.options {
    margin-bottom: 24px;
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.option-group {
    flex: 1;
}

.option-group > label {
    display: block;
    font-size: 14px;
    font-weight: 500;
    color: var(--color-text);
    margin-bottom: 8px;
}

.option-group select {
    width: 100%;
    padding: 10px 14px;
    font-size: 15px;
    font-family: inherit;
    border: 1px solid var(--color-border);
    border-radius: var(--radius-sm);
    background: var(--color-card);
    color: var(--color-text);
    cursor: pointer;
    appearance: none;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='16' height='16' viewBox='0 0 24 24' fill='none' stroke='%2364748b' stroke-width='2'%3E%3Cpolyline points='6 9 12 15 18 9'%3E%3C/polyline%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-position: right 12px center;
    padding-right: 40px;
    transition: border-color 0.2s, box-shadow 0.2s;
}

.option-group select:hover {
    border-color: var(--color-border-hover);
}

.option-group select:focus {
    outline: none;
    border-color: var(--color-primary);
    box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1);
}

/* Convert button */
.convert-btn {
    width: 100%;
    padding: 14px 20px;
    background: var(--color-primary);
    color: white;
    border: none;
    border-radius: var(--radius-sm);
    font-size: 16px;
    font-weight: 600;
    font-family: inherit;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 10px;
    transition: background 0.2s, transform 0.1s;
}

.convert-btn:hover {
    background: var(--color-primary-hover);
}

.convert-btn:active {
    transform: scale(0.98);
}

/* Divider */
.divider {
    height: 1px;
    background: var(--color-border);
    margin: 28px 0;
}

/* Instructions */
.instructions h3 {
    font-size: 14px;
    font-weight: 600;
    color: var(--color-text-muted);
    text-transform: uppercase;
    letter-spacing: 0.5px;
    margin-bottom: 16px;
}

.steps {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.step {
    display: flex;
    align-items: flex-start;
    gap: 12px;
}

.step-number {
    width: 24px;
    height: 24px;
    background: var(--color-bg);
    border: 1px solid var(--color-border);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 12px;
    font-weight: 600;
    color: var(--color-text-muted);
    flex-shrink: 0;
}

.step p {
    font-size: 14px;
    color: var(--color-text-muted);
    padding-top: 2px;
}

.step code {
    background: var(--color-bg);
    border: 1px solid var(--color-border);
    padding: 2px 6px;
    border-radius: 4px;
    font-family: 'SF Mono', 'Consolas', monospace;
    font-size: 13px;
    color: var(--color-primary);
}

/* Footer */
.footer {
    text-align: center;
    margin-top: 20px;
    padding: 0 20px;
}

.footer p {
    font-size: 13px;
    color: var(--color-text-muted);
}

/* Mobile responsiveness */
@media (max-width: 480px) {
    body {
        padding: 16px;
        align-items: flex-start;
        padding-top: 24px;
    }

    .card {
        padding: 24px;
    }

    .header h1 {
        font-size: 22px;
    }

    .upload-zone {
        padding: 32px 20px;
    }

    .option-row {
        flex-direction: column;
        gap: 12px;
    }

    .checkbox-label {
        padding-top: 0;
    }

    .logo svg {
        width: 32px;
        height: 32px;
    }

    .logo .arrow {
        width: 20px;
        height: 20px;
    }
}