:root {
    /* Modern Color Palette - Vehicle Cost Theme */
    --color-text: #2c3e50;
    --color-background: #f5f7fa;
    --color-surface: #ffffff;
    --color-primary: #e74c3c;
    --color-primary-hover: #c0392b;
    --color-success: #27ae60;
    --color-success-hover: #229954;
    --color-warning: #f39c12;
    --color-warning-hover: #d35400;
    --color-secondary: #7f8c8d;
    --color-secondary-hover: #707b7c;
    --color-border: #dfe6e9;
    --color-muted: #95a5a6;
    --color-header-bg: #e74c3c;
    --color-header-text: #ffffff;
    --color-code-bg: #ecf0f1;
    --color-highlight: #16a085;

    /* Typography */
    --font-family-sans-serif: 'Inter', sans-serif;
    --font-size-base: 1rem;
    --font-size-lg: 1.25rem;
    --font-size-sm: 0.875rem;
    --font-size-h1: 2rem;
    --font-size-h2: 1.5rem;
    --font-weight-normal: 400;
    --font-weight-bold: 700;
    --line-height-base: 1.6;

    /* Spacing */
    --spacing-1: 0.25rem;
    --spacing-2: 0.5rem;
    --spacing-3: 1rem;
    --spacing-4: 1.5rem;
    --spacing-5: 2rem;

    /* Borders */
    --border-width: 1px;
    --border-radius: 0.375rem;
    --border-radius-sm: 0.25rem;
}

* {
    box-sizing: border-box;
}

body {
    font-family: var(--font-family-sans-serif);
    line-height: var(--line-height-base);
    margin: 0;
    padding: 0;
    background-color: var(--color-background);
    color: var(--color-text);
}

/* --- Header --- */
header {
    background: var(--color-header-bg);
    padding: var(--spacing-3) var(--spacing-5);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-4);
}

#header-logo {
    max-height: 60px;
    width: auto;
}

.header-logo-link {
    text-decoration: none;
    border: none;
    outline: none;
    transition: transform 0.2s ease, opacity 0.2s ease;
}

.header-logo-link:hover {
    transform: scale(1.05);
    opacity: 0.8;
}

.header-logo-link:focus {
    outline: 2px solid var(--color-primary);
    outline-offset: 2px;
}

.header-text {
    text-align: center;
}

header h1 {
    margin: 0;
    font-size: var(--font-size-h1);
    color: #ffffff;
}

header p {
    font-size: var(--font-size-sm);
    color: #f8f9fa;
    margin: var(--spacing-1) 0 0 0;
}

.theme-toggle-btn {
    background: transparent;
    border: 2px solid #ffffff;
    border-radius: 50%;
    width: 44px;
    height: 44px;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.25rem;
    transition: transform 0.2s ease;
    flex-shrink: 0;
}

.theme-toggle-btn:hover {
    transform: scale(1.1);
}

.theme-icon-dark {
    display: none;
}

body.dark-mode .theme-icon-light {
    display: none;
}

body.dark-mode .theme-icon-dark {
    display: inline;
}

body.dark-mode .theme-toggle-btn {
    border-color: var(--color-text);
}

/* --- Main Layout --- */
main {
    padding: var(--spacing-3);
}

.container {
    max-width: 1000px;
    margin: auto;
    padding: 0 var(--spacing-5);
    width: 100%;
}

section {
    background: var(--color-surface);
    padding: var(--spacing-4);
    border-radius: var(--border-radius);
    box-shadow: 0 0 10px rgba(0,0,0,0.05);
    margin-bottom: var(--spacing-4);
}

h2 {
    color: #2c3e50;
    margin-top: 0;
    font-size: var(--font-size-h2);
    margin-bottom: var(--spacing-4);
    font-weight: 700;
    letter-spacing: 0.2px;
}

/* --- Form Elements --- */
.form-group {
    margin-bottom: var(--spacing-3);
}

.form-group label {
    display: block;
    font-weight: 600;
    margin-bottom: var(--spacing-1);
    color: #2c3e50;
    font-size: 0.95em;
    letter-spacing: 0.2px;
}

.form-group input,
.form-group select {
    width: 100%;
    padding: var(--spacing-2) var(--spacing-3);
    border: var(--border-width) solid var(--color-border);
    border-radius: var(--border-radius);
    font-size: var(--font-size-base);
    font-family: var(--font-family-sans-serif);
    background-color: var(--color-surface);
    color: var(--color-text);
}

.form-group input:focus,
.form-group select:focus {
    outline: none;
    border-color: var(--color-primary);
    box-shadow: 0 0 0 3px rgba(231, 76, 60, 0.15);
}

.form-group .hint {
    display: block;
    font-size: var(--font-size-sm);
    color: var(--color-muted);
    margin-top: var(--spacing-1);
}

.form-row {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: var(--spacing-3);
}

.form-group h3 {
    color: #e74c3c;
    font-size: 1.1em;
    margin-bottom: var(--spacing-3);
    border-bottom: 1px solid var(--color-border);
    padding-bottom: var(--spacing-2);
    font-weight: 700;
    letter-spacing: 0.3px;
}

.form-group h5 {
    color: #34495e;
    font-size: 1em;
    font-weight: 600;
    margin: var(--spacing-2) 0 var(--spacing-1) 0;
    letter-spacing: 0.1px;
}

/* --- Buttons --- */
.button {
    display: inline-block;
    padding: var(--spacing-2) var(--spacing-4);
    font-size: var(--font-size-base);
    font-weight: var(--font-weight-bold);
    cursor: pointer;
    border: none;
    border-radius: var(--border-radius);
    margin-right: var(--spacing-2);
    margin-top: var(--spacing-2);
    text-align: center;
    transition: background-color 0.15s ease-in-out;
}

.button-primary {
    background-color: var(--color-primary);
    color: var(--color-header-text);
}
.button-primary:hover {
    background-color: var(--color-primary-hover);
}

.button-success {
    background-color: var(--color-success);
    color: var(--color-header-text);
}
.button-success:hover {
    background-color: var(--color-success-hover);
}

.button-secondary {
    background-color: var(--color-secondary);
    color: var(--color-header-text);
}
.button-secondary:hover {
    background-color: var(--color-secondary-hover);
}

/* --- Results Section --- */
.results-placeholder {
    text-align: center;
    padding: var(--spacing-5);
    color: var(--color-muted);
    background: #f8f9fa;
    border-radius: var(--border-radius);
    border: 2px dashed var(--color-border);
}

.results-content {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-4);
}

.result-card {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--border-radius);
    padding: var(--spacing-4);
    display: flex;
    justify-content: space-between;
    align-items: center;
    box-shadow: 0 2px 4px rgba(0,0,0,0.05);
}

.result-primary {
    background: linear-gradient(135deg, var(--color-primary), #c0392b);
    color: white;
    border: none;
    font-size: 1.2em;
}

.result-secondary {
    background: #f8f9fa;
    border-color: var(--color-border);
}

.result-highlight {
    background: linear-gradient(135deg, var(--color-warning), #d35400);
    color: white;
    border: none;
}

.result-label {
    font-weight: 600;
    font-size: 0.9em;
    color: #5d6d7e;
    letter-spacing: 0.1px;
}

.result-value {
    font-weight: var(--font-weight-bold);
    font-size: 1.1em;
}

.result-row {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: var(--spacing-3);
}

/* --- Cost Breakdown --- */
.cost-breakdown {
    background: var(--color-code-bg);
    border-radius: var(--border-radius);
    padding: var(--spacing-3);
    margin: var(--spacing-2) 0;
}

.cost-breakdown h3 {
    margin: 0 0 var(--spacing-3) 0;
    color: var(--color-text);
    font-size: 1em;
    font-weight: var(--font-weight-bold);
}

.breakdown-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--spacing-1) 0;
    border-bottom: 1px solid var(--color-border);
}

.breakdown-item:last-child {
    border-bottom: none;
}

.breakdown-label {
    font-size: var(--font-size-sm);
    color: #5d6d7e;
    font-weight: 500;
}

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

/* --- Yearly Breakdown --- */
.yearly-breakdown {
    margin: var(--spacing-4) 0;
}

#yearlyBreakdownChart {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: var(--spacing-3);
    margin: var(--spacing-3) 0;
}

.yearly-card {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--border-radius);
    padding: var(--spacing-3);
    text-align: center;
}

.yearly-card h5 {
    margin: 0 0 var(--spacing-2) 0;
    color: var(--color-primary);
    font-size: 0.9em;
}

.yearly-card .year {
    font-size: 1.5rem;
    font-weight: var(--font-weight-bold);
    color: var(--color-text);
}

.yearly-card .cost {
    font-size: 1.1rem;
    color: var(--color-primary);
    font-weight: var(--font-weight-bold);
}

/* --- Cost Comparison --- */
.cost-comparison {
    margin: var(--spacing-4) 0;
}

.comparison-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: var(--spacing-3);
    margin: var(--spacing-3) 0;
}

.comparison-card {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--border-radius);
    padding: var(--spacing-3);
    text-align: center;
}

.comparison-card h4 {
    margin: 0 0 var(--spacing-2) 0;
    color: var(--color-text);
    font-size: 1em;
    font-weight: var(--font-weight-bold);
}

.comparison-value {
    font-size: 1.3rem;
    font-weight: var(--font-weight-bold);
    color: var(--color-primary);
    margin: var(--spacing-1) 0;
}

.comparison-detail {
    font-size: var(--font-size-sm);
    color: var(--color-muted);
    margin: 0;
}

/* --- Insight Box --- */
.insight-box {
    background: linear-gradient(135deg, #3498db, #2980b9);
    color: white;
    border-radius: var(--border-radius);
    padding: var(--spacing-4);
    margin: var(--spacing-4) 0;
}

.insight-box h3 {
    margin: 0 0 var(--spacing-2) 0;
    color: white;
}

.insight-box p {
    margin: 0;
    line-height: 1.6;
}

/* --- Download Section --- */
.download-section {
    display: flex;
    align-items: center;
    gap: var(--spacing-2);
    margin-top: var(--spacing-3);
}

/* --- Mode Toggle --- */
.mode-toggle {
    display: flex;
    justify-content: center;
    gap: var(--spacing-2);
    margin-bottom: var(--spacing-4);
    padding: var(--spacing-2);
    background: var(--color-code-bg);
    border-radius: var(--border-radius);
    border: 1px solid var(--color-border);
}

.mode-btn {
    padding: var(--spacing-2) var(--spacing-4);
    border: 2px solid var(--color-border);
    background: var(--color-surface);
    color: var(--color-text);
    border-radius: var(--border-radius);
    cursor: pointer;
    font-weight: var(--font-weight-bold);
    transition: all 0.2s ease;
    font-size: 0.9rem;
}

.mode-btn:hover {
    background: var(--color-secondary);
    color: white;
}

.mode-btn.active {
    background: var(--color-primary);
    color: var(--color-header-text);
    border-color: var(--color-primary);
}

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

/* --- Quick Calculator Section --- */
#quickCalculatorSection {
    background: linear-gradient(135deg, #f8f9fa, #e9ecef);
    border: 2px solid var(--color-primary);
    border-radius: var(--border-radius);
    padding: var(--spacing-4);
    margin-bottom: var(--spacing-3);
}

.quick-description {
    text-align: center;
    color: var(--color-muted);
    margin-bottom: var(--spacing-3);
    font-style: italic;
}

/* --- Advanced Calculator Section --- */
#advancedCalculatorSection {
    border: 1px solid var(--color-border);
    border-radius: var(--border-radius);
    padding: var(--spacing-2);
    margin-bottom: var(--spacing-3);
}

.advanced-description {
    text-align: center;
    color: var(--color-muted);
    margin-bottom: var(--spacing-3);
    font-style: italic;
}

/* --- RUC Section --- */
.ruc-info {
    background: linear-gradient(135deg, #e8f4f8, #d1e7dd);
    border-left: 4px solid var(--color-primary);
    padding: var(--spacing-2);
    margin-bottom: var(--spacing-3);
    border-radius: 0 var(--border-radius) var(--border-radius) 0;
}

.ruc-description {
    margin: 0;
    color: var(--color-text);
    font-size: 0.9rem;
    font-weight: var(--font-weight-medium);
}

/* --- Related Tools --- */
.related-tool-link {
    color: var(--color-primary);
    text-decoration: underline;
    font-weight: var(--font-weight-bold);
}

.related-tool-link:hover {
    color: var(--color-primary-hover);
}

.related-tool-button {
    margin-top: var(--spacing-3);
    text-align: center;
}

.related-tool-button .button {
    width: 100%;
    max-width: 300px;
}

/* --- Help Section --- */
.help-article {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--border-radius);
    padding: var(--spacing-4);
    margin-bottom: var(--spacing-3);
}

.help-article h3 {
    margin: 0 0 var(--spacing-3) 0;
    color: var(--color-primary);
}

.help-article ul {
    margin: var(--spacing-2) 0;
    padding-left: var(--spacing-4);
}

.help-article li {
    margin: var(--spacing-1) 0;
}

/* --- Back Section --- */
.back-section {
    text-align: center;
    margin: var(--spacing-4) 0;
}

.back-link {
    margin-top: var(--spacing-4);
}

/* --- Footer --- */
footer {
    background: var(--color-header-bg);
    color: white;
    text-align: center;
    padding: var(--spacing-4);
    margin-top: var(--spacing-5);
}

footer p {
    margin: var(--spacing-1) 0;
}

footer a {
    color: white;
    text-decoration: underline;
}

footer a:hover {
    text-decoration: none;
}

.visitor-count {
    vertical-align: middle;
}

/* --- Hidden Elements --- */
.hidden {
    display: none;
}

.sr-only {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0,0,0,0);
    white-space: nowrap;
    border: 0;
}

/* --- Responsive Design --- */
@media (max-width: 768px) {
    .container {
        padding: 0 var(--spacing-3);
    }
    
    main {
        padding: var(--spacing-2);
    }
    
    header {
        flex-direction: column;
        text-align: center;
        gap: var(--spacing-2);
        padding: var(--spacing-2) var(--spacing-3);
    }
    
    #header-logo {
        max-height: 50px;
    }
    
    header h1 {
        font-size: 1.5rem;
    }
    
    header p {
        font-size: 0.8rem;
    }
    
    .form-row {
        grid-template-columns: 1fr;
    }
    
    .result-row {
        grid-template-columns: 1fr;
    }
    
    .comparison-grid {
        grid-template-columns: 1fr;
    }
    
    #yearlyBreakdownChart {
        grid-template-columns: 1fr;
    }
    
    .download-section {
        flex-direction: column;
        gap: var(--spacing-1);
    }
    
    .button {
        width: 100%;
        margin-right: 0;
    }
}

@media (max-width: 480px) {
    header {
        padding: var(--spacing-1);
    }
    
    #header-logo {
        max-height: 40px;
    }
    
    header h1 {
        font-size: 1.25rem;
    }
    
    header p {
        font-size: 0.75rem;
    }
    
    section {
        padding: var(--spacing-3);
    }
    
    .result-card {
        flex-direction: column;
        text-align: center;
        gap: var(--spacing-1);
    }
    
    .result-value {
        font-size: 1rem;
    }
    
    .cost-breakdown {
        padding: var(--spacing-2);
    }
    
    .breakdown-item {
        flex-direction: column;
        align-items: flex-start;
        gap: var(--spacing-1);
    }
}

/* --- Dark Mode --- */
.dark-mode {
    --color-text: #ecf0f1;
    --color-background: #2c3e50;
    --color-surface: #34495e;
    --color-primary: #e74c3c;
    --color-primary-hover: #c0392b;
    --color-success: #52be80;
    --color-success-hover: #7dcea0;
    --color-warning: #f39c12;
    --color-warning-hover: #f7dc6f;
    --color-secondary: #aeb6bf;
    --color-secondary-hover: #d5d8dc;
    --color-border: #5d6d7e;
    --color-muted: #aeb6bf;
    --color-header-bg: #c0392b;
    --color-header-text: #ecf0f1;
    --color-code-bg: #34495e;
}

/* Enhanced contrast for dark mode form labels */
.dark-mode .form-group label {
    color: #f8f9fa;
    font-weight: 600;
}

.dark-mode .form-group h3 {
    color: #ff6b6b;
    font-weight: 700;
}

.dark-mode .form-group h5 {
    color: #f8f9fa;
    font-weight: 600;
}

.dark-mode h2 {
    color: #f8f9fa;
    font-weight: 700;
}

.dark-mode .breakdown-label {
    color: #bdc3c7;
    font-weight: 500;
}

.dark-mode .result-label {
    color: #bdc3c7;
    font-weight: 600;
}

.dark-mode .form-group input,
.dark-mode .form-group select {
    background-color: var(--color-surface);
    color: var(--color-text);
    border-color: var(--color-border);
}

.dark-mode .results-placeholder {
    background: var(--color-surface);
    border-color: var(--color-border);
    color: var(--color-muted);
}

.dark-mode .result-card {
    background: var(--color-surface);
    border-color: var(--color-border);
}

.dark-mode .result-secondary {
    background: var(--color-code-bg);
}

.dark-mode .cost-breakdown {
    background: var(--color-surface);
    border: 1px solid var(--color-border);
}

.dark-mode .yearly-card,
.dark-mode .comparison-card {
    background: var(--color-surface);
    border-color: var(--color-border);
}

.dark-mode #quickCalculatorSection {
    background: var(--color-surface);
    border-color: var(--color-primary);
}

.dark-mode #advancedCalculatorSection {
    background: var(--color-surface);
    border-color: var(--color-border);
}

.dark-mode .ruc-info {
    background: var(--color-surface);
    border-left-color: var(--color-primary);
}

.dark-mode .ruc-description {
    color: var(--color-text);
}

.dark-mode section {
    background: var(--color-surface);
    border-color: var(--color-border);
}

.dark-mode .help-article {
    background: var(--color-surface);
    border-color: var(--color-border);
}