/* CSS Custom Properties */
:root {
    /* Colors using HSL format */
    --primary: 220 90% 56%; /* #1E40AF */
    --primary-light: 220 90% 65%; /* #3B82F6 */
    --secondary: 160 60% 45%; /* #059669 */
    --background: 210 11% 98%; /* #F5F7FA */
    --surface: 0 0% 100%; /* #FFFFFF */
    --surface-alt: 210 11% 96%; /* #F1F5F9 */
    --text-primary: 210 11% 15%; /* #1E293B */
    --text-secondary: 210 7% 46%; /* #64748B */
    --text-muted: 210 9% 31%; /* #475569 */
    --border: 210 12% 87%; /* #CBD5E1 */
    --border-light: 210 14% 91%; /* #E2E8F0 */
    --success: 142 71% 45%; /* #10B981 */
    --error: 0 84% 60%; /* #EF4444 */
    --warning: 45 93% 47%; /* #F59E0B */
    
    /* Spacing */
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;
    
    /* Typography */
    --font-size-sm: 0.875rem;
    --font-size-base: 1rem;
    --font-size-lg: 1.125rem;
    --font-size-xl: 1.25rem;
    --font-size-2xl: 1.5rem;
    --font-size-3xl: 1.875rem;
    
    /* Border radius */
    --radius-sm: 0.375rem;
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --radius-xl: 1rem;
    
    /* Shadows */
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
    
    /* Transitions */
    --transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1);
    --transition-fast: all 0.15s cubic-bezier(0.4, 0, 0.2, 1);
}

/* Reset and base styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    background-color: hsl(var(--background));
    color: hsl(var(--text-primary));
    line-height: 1.6;
    font-size: var(--font-size-base);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* Container */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: var(--spacing-lg);
    flex: 1;
    display: flex;
    flex-direction: column;
}

/* Navigation */
.navigation {
    display: flex;
    justify-content: center;
    gap: var(--spacing-lg);
    margin-bottom: var(--spacing-xl);
    padding: var(--spacing-md) 0;
    border-bottom: 1px solid hsl(var(--border-light));
}

.nav-link {
    padding: var(--spacing-sm) var(--spacing-lg);
    border-radius: var(--radius-md);
    text-decoration: none;
    color: hsl(var(--text-secondary));
    font-weight: 500;
    transition: var(--transition);
    border: 1px solid transparent;
}

.nav-link:hover {
    color: hsl(var(--primary));
    background: hsl(var(--surface-alt));
    border-color: hsl(var(--border));
}

.nav-link.active {
    color: white;
    background: hsl(var(--primary));
    border-color: hsl(var(--primary));
}

/* Header */
.header {
    text-align: center;
    margin-bottom: var(--spacing-2xl);
    padding: var(--spacing-xl) 0;
}

.title {
    font-size: var(--font-size-3xl);
    font-weight: 700;
    color: hsl(var(--primary));
    margin-bottom: var(--spacing-sm);
    letter-spacing: -0.025em;
}

.subtitle {
    font-size: var(--font-size-lg);
    color: hsl(var(--text-secondary));
    font-weight: 400;
}

/* Main content */
.main-content {
    flex: 1;
    display: grid;
    gap: var(--spacing-2xl);
    grid-template-columns: repeat(auto-fit, minmax(350px, 1fr));
}

/* Calculator sections */
.calculator-section {
    background: hsl(var(--surface));
    border-radius: var(--radius-xl);
    padding: var(--spacing-xl);
    box-shadow: var(--shadow-md);
    border: 1px solid hsl(var(--border-light));
    transition: var(--transition);
    position: relative;
    overflow: hidden;
}

.calculator-section::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 4px;
    background: linear-gradient(90deg, hsl(var(--primary)), hsl(var(--secondary)));
    opacity: 0;
    transition: var(--transition);
}

.calculator-section:hover {
    box-shadow: var(--shadow-lg);
    transform: translateY(-2px);
}

.calculator-section:hover::before {
    opacity: 1;
}

.section-header {
    margin-bottom: var(--spacing-xl);
}

.section-title {
    font-size: var(--font-size-xl);
    font-weight: 600;
    color: hsl(var(--text-primary));
    margin-bottom: var(--spacing-xs);
}

.section-description {
    font-size: var(--font-size-sm);
    color: hsl(var(--text-secondary));
    font-weight: 400;
}

/* Calculator forms */
.calculator-form {
    display: grid;
    grid-template-columns: 1fr auto 1fr auto 1fr;
    gap: var(--spacing-md);
    align-items: end;
    margin-bottom: var(--spacing-lg);
}

.input-group {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-xs);
}

.input-label {
    font-size: var(--font-size-sm);
    font-weight: 500;
    color: hsl(var(--text-muted));
    margin-bottom: var(--spacing-xs);
}

.input-field {
    padding: var(--spacing-md) var(--spacing-lg);
    border: 2px solid hsl(var(--border));
    border-radius: var(--radius-md);
    font-size: var(--font-size-base);
    background: hsl(var(--surface));
    color: hsl(var(--text-primary));
    transition: var(--transition);
    outline: none;
    width: 100%;
    font-weight: 500;
}

.input-field:focus {
    border-color: hsl(var(--primary));
    box-shadow: 0 0 0 3px hsla(var(--primary), 0.1);
    background: hsl(var(--surface));
}

.input-field:hover {
    border-color: hsl(var(--primary-light));
}

.input-field::placeholder {
    color: hsl(var(--text-secondary));
    opacity: 0.7;
}

.operator {
    font-size: var(--font-size-sm);
    font-weight: 500;
    color: hsl(var(--text-secondary));
    text-align: center;
    padding: var(--spacing-sm);
    background: hsl(var(--surface-alt));
    border-radius: var(--radius-sm);
    align-self: center;
    white-space: nowrap;
}

.equals {
    font-size: var(--font-size-lg);
    font-weight: 600;
    color: hsl(var(--primary));
    text-align: center;
    align-self: center;
}

.result-container {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--spacing-xs);
}

.result {
    font-size: var(--font-size-2xl);
    font-weight: 700;
    color: hsl(var(--primary));
    background: linear-gradient(135deg, hsl(var(--primary)), hsl(var(--secondary)));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    text-align: center;
    min-height: 2.5rem;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: var(--transition);
}

.result-label {
    font-size: var(--font-size-sm);
    font-weight: 500;
    color: hsl(var(--text-secondary));
    text-align: center;
}

/* Operation toggle for add/subtract */
.operation-toggle {
    display: flex;
    background: hsl(var(--surface-alt));
    border-radius: var(--radius-md);
    padding: var(--spacing-xs);
    align-self: center;
}

.operation-btn {
    padding: var(--spacing-sm) var(--spacing-md);
    border: none;
    background: transparent;
    color: hsl(var(--text-secondary));
    font-size: var(--font-size-lg);
    font-weight: 600;
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: var(--transition);
    min-width: 2.5rem;
    display: flex;
    align-items: center;
    justify-content: center;
}

.operation-btn:hover {
    background: hsl(var(--surface));
    color: hsl(var(--text-primary));
}

.operation-btn.active {
    background: hsl(var(--primary));
    color: white;
    box-shadow: var(--shadow-sm);
}

/* Breakdown section */
.breakdown {
    background: hsl(var(--surface-alt));
    border-radius: var(--radius-md);
    padding: var(--spacing-lg);
    margin-top: var(--spacing-md);
    opacity: 0;
    transition: var(--transition);
}

.breakdown.show {
    opacity: 1;
}

.breakdown-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--spacing-sm) 0;
}

.breakdown-item:not(:last-child) {
    border-bottom: 1px solid hsl(var(--border-light));
}

.breakdown-label {
    font-size: var(--font-size-sm);
    color: hsl(var(--text-secondary));
    font-weight: 500;
}

.breakdown-value {
    font-size: var(--font-size-base);
    color: hsl(var(--text-primary));
    font-weight: 600;
}

/* Result animations */
.result.updated {
    animation: resultPulse 0.3s ease-out;
}

@keyframes resultPulse {
    0% { transform: scale(1); }
    50% { transform: scale(1.05); }
    100% { transform: scale(1); }
}

/* Change type colors */
.result.increase {
    background: linear-gradient(135deg, hsl(var(--success)), hsl(var(--success)));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.result.decrease {
    background: linear-gradient(135deg, hsl(var(--error)), hsl(var(--error)));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

/* Footer */
.footer {
    margin-top: var(--spacing-2xl);
    padding: var(--spacing-xl) 0;
    text-align: center;
    color: hsl(var(--text-secondary));
    font-size: var(--font-size-sm);
    border-top: 1px solid hsl(var(--border-light));
}

/* Responsive design */
@media (max-width: 768px) {
    .container {
        padding: var(--spacing-md);
    }
    
    .navigation {
        flex-direction: column;
        gap: var(--spacing-sm);
    }
    
    .nav-link {
        text-align: center;
    }
    
    .main-content {
        grid-template-columns: 1fr;
        gap: var(--spacing-xl);
    }
    
    .calculator-form {
        grid-template-columns: 1fr;
        gap: var(--spacing-lg);
        text-align: center;
    }
    
    .operator,
    .equals {
        align-self: center;
        margin: var(--spacing-sm) 0;
    }
    
    .title {
        font-size: var(--font-size-2xl);
    }
    
    .subtitle {
        font-size: var(--font-size-base);
    }
    
    .calculator-section {
        padding: var(--spacing-lg);
    }
}

@media (max-width: 480px) {
    .container {
        padding: var(--spacing-sm);
    }
    
    .header {
        margin-bottom: var(--spacing-xl);
        padding: var(--spacing-lg) 0;
    }
    
    .calculator-section {
        padding: var(--spacing-md);
    }
    
    .input-field {
        padding: var(--spacing-sm) var(--spacing-md);
    }
    
    .result {
        font-size: var(--font-size-xl);
    }
}

/* Focus styles for accessibility */
.input-field:focus-visible,
.operation-btn:focus-visible {
    outline: 2px solid hsl(var(--primary));
    outline-offset: 2px;
}

/* High contrast mode support */
@media (prefers-contrast: high) {
    :root {
        --border: 210 12% 70%;
        --text-secondary: 210 7% 30%;
    }
}

/* Reduced motion support */
@media (prefers-reduced-motion: reduce) {
    * {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
}

/* Print styles */
@media print {
    .calculator-section {
        box-shadow: none;
        border: 1px solid hsl(var(--border));
    }
    
    .footer {
        display: none;
    }
}