/* ==========================================
   CSS Variables & Design System
   ========================================== */
:root {
    /* Colors */
    --primary-color: #667eea;
    --primary-dark: #5568d3;
    --secondary-color: #764ba2;
    --accent-color: #f093fb;
    --success-color: #10b981;
    --warning-color: #f59e0b;
    --danger-color: #ef4444;
    
    /* Gradients */
    --gradient-primary: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    --gradient-bg: linear-gradient(135deg, #667eea 0%, #764ba2 50%, #f093fb 100%);
    --gradient-card: linear-gradient(135deg, rgba(255, 255, 255, 0.9) 0%, rgba(255, 255, 255, 0.8) 100%);
    
    /* Spacing */
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 1.5rem;
    --spacing-lg: 2rem;
    --spacing-xl: 3rem;
    
    /* Typography */
    --font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    --font-size-base: 16px;
    --font-size-sm: 0.875rem;
    --font-size-lg: 1.125rem;
    --font-size-xl: 1.5rem;
    --font-size-2xl: 2rem;
    
    /* Shadows */
    --shadow-sm: 0 2px 4px rgba(0, 0, 0, 0.1);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 25px rgba(0, 0, 0, 0.15);
    --shadow-xl: 0 20px 40px rgba(0, 0, 0, 0.2);
    
    /* Border Radius */
    --radius-sm: 0.5rem;
    --radius-md: 1rem;
    --radius-lg: 1.5rem;
    
    /* Transitions */
    --transition-fast: 0.2s ease;
    --transition-normal: 0.3s ease;
    --transition-slow: 0.5s ease;
}

/* ==========================================
   Reset & Base Styles
   ========================================== */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: var(--font-family);
    font-size: var(--font-size-base);
    line-height: 1.6;
    color: #333;
    background: var(--gradient-bg);
    background-attachment: fixed;
    min-height: 100vh;
    overflow-x: hidden;
}

/* ==========================================
   Container & Layout
   ========================================== */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: var(--spacing-lg);
}

/* ==========================================
   Header
   ========================================== */
header {
    text-align: center;
    margin-bottom: var(--spacing-xl);
    padding: var(--spacing-lg) 0;
}

header h1 {
    font-size: var(--font-size-2xl);
    font-weight: 700;
    color: white;
    margin-bottom: var(--spacing-sm);
    text-shadow: 0 2px 10px rgba(0, 0, 0, 0.2);
    animation: fadeInDown 0.6s ease;
}

.subtitle {
    font-size: var(--font-size-lg);
    color: rgba(255, 255, 255, 0.95);
    font-weight: 500;
    animation: fadeInUp 0.6s ease;
}

/* ==========================================
   Cards
   ========================================== */
.card {
    background: var(--gradient-card);
    backdrop-filter: blur(10px);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    box-shadow: var(--shadow-lg);
    margin-bottom: var(--spacing-lg);
    border: 1px solid rgba(255, 255, 255, 0.3);
    animation: fadeInUp 0.6s ease;
    transition: transform var(--transition-normal), box-shadow var(--transition-normal);
}

.card:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-xl);
}

.card h2 {
    font-size: var(--font-size-xl);
    color: var(--primary-color);
    margin-bottom: var(--spacing-md);
    font-weight: 700;
}

.card h3 {
    font-size: var(--font-size-lg);
    color: var(--secondary-color);
    margin-bottom: var(--spacing-sm);
    font-weight: 600;
}

/* ==========================================
   Form Styles
   ========================================== */
.form-group {
    margin-bottom: var(--spacing-md);
}

.form-group label {
    display: block;
    font-weight: 600;
    color: #333;
    margin-bottom: var(--spacing-xs);
    font-size: var(--font-size-base);
}

.form-group input {
    width: 100%;
    padding: 0.875rem 1rem;
    border: 2px solid #e5e7eb;
    border-radius: var(--radius-sm);
    font-size: var(--font-size-base);
    font-family: var(--font-family);
    transition: all var(--transition-normal);
    background: white;
}

.form-group input:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(102, 126, 234, 0.1);
    transform: translateY(-2px);
}

.form-group input:hover {
    border-color: var(--primary-dark);
}

.hint {
    display: block;
    font-size: var(--font-size-sm);
    color: #6b7280;
    margin-top: var(--spacing-xs);
    font-style: italic;
}

/* ==========================================
   Buttons
   ========================================== */
.btn-calculate {
    width: 100%;
    padding: 1rem 2rem;
    background: var(--gradient-primary);
    color: white;
    border: none;
    border-radius: var(--radius-sm);
    font-size: var(--font-size-lg);
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition-normal);
    box-shadow: var(--shadow-md);
    margin-top: var(--spacing-sm);
    font-family: var(--font-family);
}

.btn-calculate:hover {
    transform: translateY(-3px);
    box-shadow: var(--shadow-lg);
}

.btn-calculate:active {
    transform: translateY(-1px);
}

/* ==========================================
   Result Card
   ========================================== */
.result-card {
    margin-top: var(--spacing-lg);
    padding: var(--spacing-lg);
    background: linear-gradient(135deg, #f0f9ff 0%, #e0f2fe 100%);
    border-radius: var(--radius-md);
    border: 2px solid var(--primary-color);
    animation: slideInUp 0.5s ease;
}

.result-card h3 {
    text-align: center;
    color: var(--primary-color);
    margin-bottom: var(--spacing-md);
    font-size: var(--font-size-xl);
}

.result-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: var(--spacing-md);
}

.result-item {
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: var(--spacing-md);
    background: white;
    border-radius: var(--radius-sm);
    box-shadow: var(--shadow-sm);
    transition: transform var(--transition-fast);
}

.result-item:hover {
    transform: scale(1.05);
}

.result-label {
    font-size: var(--font-size-sm);
    color: #6b7280;
    margin-bottom: var(--spacing-xs);
    font-weight: 500;
}

.result-value {
    font-size: var(--font-size-xl);
    font-weight: 700;
    color: #333;
}

.result-value.success {
    color: var(--success-color);
}

.result-value.danger {
    color: var(--danger-color);
}

.result-value.highlight {
    color: var(--primary-color);
}

/* ==========================================
   Formula Section
   ========================================== */
.formula-box {
    margin-bottom: var(--spacing-lg);
    padding: var(--spacing-md);
    background: rgba(102, 126, 234, 0.05);
    border-radius: var(--radius-sm);
    border-left: 4px solid var(--primary-color);
}

.formula {
    font-family: 'Courier New', monospace;
    font-size: var(--font-size-base);
    line-height: 2;
}

.formula p {
    margin-bottom: var(--spacing-xs);
    color: #333;
}

.formula strong {
    color: var(--primary-color);
}

/* ==========================================
   Tax Table
   ========================================== */
.tax-table {
    width: 100%;
    border-collapse: collapse;
    margin-top: var(--spacing-md);
    background: white;
    border-radius: var(--radius-sm);
    overflow: hidden;
    box-shadow: var(--shadow-sm);
}

.tax-table thead {
    background: var(--gradient-primary);
    color: white;
}

.tax-table th,
.tax-table td {
    padding: 1rem;
    text-align: left;
    border-bottom: 1px solid #e5e7eb;
}

.tax-table th {
    font-weight: 600;
    font-size: var(--font-size-base);
}

.tax-table tbody tr {
    transition: background-color var(--transition-fast);
}

.tax-table tbody tr:hover {
    background-color: rgba(102, 126, 234, 0.05);
}

.tax-table tbody tr:last-child td {
    border-bottom: none;
}

.tax-table .success {
    color: var(--success-color);
    font-weight: 600;
}

.tax-table .warning {
    color: var(--warning-color);
    font-weight: 600;
}

.tax-table .danger {
    color: var(--danger-color);
    font-weight: 600;
}

/* ==========================================
   Examples Section
   ========================================== */
.example-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: var(--spacing-md);
    margin-top: var(--spacing-md);
}

.example-card {
    padding: var(--spacing-md);
    background: linear-gradient(135deg, #fef3c7 0%, #fde68a 100%);
    border-radius: var(--radius-md);
    border: 2px solid #fbbf24;
    transition: transform var(--transition-normal);
}

.example-card:hover {
    transform: translateY(-5px);
}

.example-card h3 {
    color: #92400e;
    margin-bottom: var(--spacing-sm);
    font-size: var(--font-size-lg);
}

.example-content p {
    margin-bottom: var(--spacing-sm);
    color: #78350f;
    font-weight: 500;
}

.example-content ul {
    list-style: none;
    padding-left: 0;
}

.example-content li {
    padding: var(--spacing-xs) 0;
    color: #78350f;
    position: relative;
    padding-left: 1.5rem;
}

.example-content li::before {
    content: "▸";
    position: absolute;
    left: 0;
    color: #f59e0b;
    font-weight: bold;
}

/* ==========================================
   Explanation Section
   ========================================== */
.explanation-content h3 {
    color: var(--primary-color);
    margin-top: var(--spacing-lg);
    margin-bottom: var(--spacing-sm);
    font-size: var(--font-size-lg);
}

.explanation-content h3:first-child {
    margin-top: 0;
}

.explanation-content p {
    margin-bottom: var(--spacing-md);
    color: #4b5563;
    line-height: 1.8;
}

.explanation-content ul,
.explanation-content ol {
    margin-bottom: var(--spacing-md);
    padding-left: var(--spacing-lg);
    color: #4b5563;
}

.explanation-content li {
    margin-bottom: var(--spacing-xs);
    line-height: 1.8;
}

.explanation-content strong {
    color: var(--primary-color);
    font-weight: 600;
}

.notice-box {
    background: linear-gradient(135deg, #fef2f2 0%, #fee2e2 100%);
    border-left: 4px solid var(--danger-color);
    padding: var(--spacing-md);
    border-radius: var(--radius-sm);
    margin-top: var(--spacing-md);
}

.notice-box p {
    color: #991b1b;
    font-weight: 600;
    margin-bottom: var(--spacing-sm);
}

.notice-box ul {
    color: #7f1d1d;
}

/* ==========================================
   Ad Section
   ========================================== */
.ad-section {
    margin: var(--spacing-xl) 0;
    min-height: 100px;
    display: flex;
    align-items: center;
    justify-content: center;
}

/* ==========================================
   Footer
   ========================================== */
footer {
    text-align: center;
    padding: var(--spacing-lg) 0;
    color: rgba(255, 255, 255, 0.9);
    font-size: var(--font-size-sm);
    margin-top: var(--spacing-xl);
}

/* ==========================================
   Animations
   ========================================== */
@keyframes fadeInDown {
    from {
        opacity: 0;
        transform: translateY(-20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@keyframes slideInUp {
    from {
        opacity: 0;
        transform: translateY(30px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* ==========================================
   Responsive Design
   ========================================== */
@media (max-width: 768px) {
    :root {
        --font-size-2xl: 1.5rem;
        --font-size-xl: 1.25rem;
        --font-size-lg: 1rem;
    }
    
    .container {
        padding: var(--spacing-sm);
    }
    
    .card {
        padding: var(--spacing-md);
    }
    
    header h1 {
        font-size: 1.75rem;
    }
    
    .result-grid {
        grid-template-columns: 1fr;
    }
    
    .example-grid {
        grid-template-columns: 1fr;
    }
    
    .tax-table {
        font-size: var(--font-size-sm);
    }
    
    .tax-table th,
    .tax-table td {
        padding: 0.75rem 0.5rem;
    }
}

@media (max-width: 480px) {
    header h1 {
        font-size: 1.5rem;
    }
    
    .subtitle {
        font-size: var(--font-size-base);
    }
    
    .btn-calculate {
        font-size: var(--font-size-base);
    }
}