:root {
    --primary: #4f46e5;
    --primary-hover: #4338ca;
    --bg-gradient-start: #f3f4f6;
    --bg-gradient-end: #e5e7eb;
    --card-bg: #ffffff;
    --text-main: #1f2937;
    --text-muted: #6b7280;
    --border: #e5e7eb;
    --success: #10b981;
    --error: #ef4444;
}

body {
    font-family: 'Inter', system-ui, -apple-system, sans-serif;
    background: linear-gradient(135deg, var(--bg-gradient-start) 0%, var(--bg-gradient-end) 100%);
    min-height: 100vh;
    margin: 0;
    padding: 2rem;
    color: var(--text-main);
    display: flex;
    justify-content: center;
    align-items: flex-start;
}

.container {
    width: 100%;
    max-width: 800px;
}

/* Header */
header {
    text-align: center;
    margin-bottom: 2rem;
}

header h1 {
    font-size: 2.5rem;
    font-weight: 800;
    background: linear-gradient(to right, var(--primary), #818cf8);
    -webkit-background-clip: text;
    background-clip: text;
    -webkit-text-fill-color: transparent;
    margin-bottom: 0.5rem;
}

header p {
    color: var(--text-muted);
}

/* Main Card */
.app-card {
    background: var(--card-bg);
    border-radius: 1.5rem;
    box-shadow: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
    overflow: hidden;
    backdrop-filter: blur(10px);
}

/* Tabs */
.tabs {
    display: flex;
    border-bottom: 1px solid var(--border);
    background: #f9fafb;
}

.tab-btn {
    flex: 1;
    padding: 1rem;
    border: none;
    background: none;
    font-weight: 600;
    color: var(--text-muted);
    cursor: pointer;
    transition: all 0.2s;
    border-bottom: 3px solid transparent;
}

.tab-btn:hover {
    color: var(--primary);
    background: rgba(79, 70, 229, 0.05);
}

.tab-btn.active {
    color: var(--primary);
    border-bottom-color: var(--primary);
    background: #fff;
}

/* Content */
.tab-content {
    display: none;
    padding: 2rem;
    animation: fadeIn 0.3s ease;
}

.tab-content.active {
    display: block;
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(5px);
    }

    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* Forms */
.form-group {
    margin-bottom: 1.5rem;
}

label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 600;
    color: var(--text-main);
}

input[type="file"],
input[type="text"],
input[type="number"],
select {
    width: 100%;
    padding: 0.75rem;
    border: 1px solid var(--border);
    border-radius: 0.5rem;
    background: #fff;
    transition: border-color 0.2s, box-shadow 0.2s;
    box-sizing: border-box;
}

input[type="file"] {
    padding: 0.5rem;
    background: #f9fafb;
}

input:focus,
select:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 3px rgba(79, 70, 229, 0.1);
}

.btn-primary {
    display: block;
    width: 100%;
    padding: 1rem;
    background: var(--primary);
    color: white;
    border: none;
    border-radius: 0.75rem;
    font-weight: 600;
    font-size: 1rem;
    cursor: pointer;
    transition: transform 0.1s, box-shadow 0.2s, background-color 0.2s;
}

.btn-primary:hover {
    background-color: var(--primary-hover);
    box-shadow: 0 4px 6px -1px rgba(79, 70, 229, 0.3);
}

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

/* Alerts */
.alert {
    padding: 1rem;
    border-radius: 0.75rem;
    margin-bottom: 1.5rem;
    font-size: 0.9rem;
}

.alert-error {
    background-color: #fef2f2;
    color: #991b1b;
    border: 1px solid #fecaca;
}

.alert-info {
    background-color: #eff6ff;
    color: #1e40af;
    border: 1px solid #dbeafe;
}

.hint {
    color: var(--text-muted);
    font-size: 0.8rem;
    margin-top: 0.3rem;
    display: block;
}

/* File List for Merge */
.file-list {
    margin-top: 0.5rem;
    border: 1px dashed var(--border);
    border-radius: 0.5rem;
    padding: 1rem;
    background: #fafafa;
}

/* Footer */
footer {
    text-align: center;
    margin-top: 2rem;
    color: var(--text-muted);
    font-size: 0.8rem;
}

/* Diagnostic Box */
.diagnostic-box {
    margin-top: 2rem;
    padding: 1.5rem;
    background: #1f2937;
    color: #f3f4f6;
    border-radius: 1rem;
    font-family: monospace;
    font-size: 0.85rem;
    line-height: 1.5;
}

.diagnostic-box h3 {
    color: #ef4444;
    margin-top: 0;
}