:root {
    --primary-color: #3b82f6;
    --primary-hover: #2563eb;
    --bg-color: #f8fafc;
    --surface-color: #ffffff;
    --border-color: #e2e8f0;
    --text-primary: #0f172a;
    --text-secondary: #64748b;
    --text-muted: #94a3b8;
    --success-color: #10b981;
    --warning-color: #f59e0b;
    --error-color: #ef4444;
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.07), 0 2px 4px -2px rgba(0, 0, 0, 0.05);
    --radius-sm: 6px;
    --radius-md: 8px;
    --radius-lg: 12px;
    --transition: 200ms ease;
}

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

html,
body {
    background-color: var(--bg-color);
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Inter', 'Roboto', sans-serif;
    color: var(--text-primary);
    line-height: 1.5;
}

/* ========== App Layout ========== */
.app-layout {
    display: grid;
    grid-template-columns: 320px 1fr;
    min-height: 100vh;
}

/* ========== Sidebar ========== */
.sidebar {
    background: var(--surface-color);
    border-right: 1px solid var(--border-color);
    display: flex;
    flex-direction: column;
    position: sticky;
    top: 0;
    height: 100vh;
    overflow: hidden;
}

.sidebar-header {
    padding: 1.25rem 1rem;
    border-bottom: 1px solid var(--border-color);
    flex-shrink: 0;
}

.sidebar-header h1 {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 0.125rem;
}

.sidebar-header .subtitle {
    font-size: 0.75rem;
    color: var(--text-secondary);
}

.sidebar-content {
    padding: 1rem;
    flex: 1;
    overflow-y: auto;
}

/* ========== Hero Input (Monthly Minutes) ========== */
.input-section--hero {
    background: linear-gradient(135deg, #eff6ff 0%, #f0fdf4 100%);
    padding: 1rem;
    border-radius: var(--radius-md);
    margin-bottom: 1rem;
    border: 1px solid #dbeafe;
}

.input-label-hero {
    display: block;
    font-size: 0.6875rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-secondary);
    margin-bottom: 0.375rem;
}

.input-hero {
    width: 100%;
    padding: 0.625rem 0.75rem;
    font-size: 1.125rem;
    font-weight: 600;
    background: var(--surface-color);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    color: var(--text-primary);
    transition: border-color var(--transition), box-shadow var(--transition);
}

.input-hero:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.1);
}

.time-period-row {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    margin-top: 0.5rem;
    font-size: 0.75rem;
    color: var(--text-secondary);
}

.time-period-row input[type="number"] {
    width: 60px;
    padding: 0.375rem 0.5rem;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    font-size: 0.8125rem;
    font-weight: 600;
    background: var(--surface-color);
    text-align: center;
}

.time-period-row input[type="number"]:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 2px rgba(59, 130, 246, 0.1);
}

.input-hint {
    display: block;
    font-size: 0.6875rem;
    color: var(--text-muted);
    margin-top: 0.375rem;
}

/* ========== Accordion Sections ========== */
.input-accordion {
    margin-bottom: 0.5rem;
    border-radius: var(--radius-md);
    overflow: hidden;
}

.accordion-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0.75rem 0.875rem;
    background: var(--bg-color);
    border-radius: var(--radius-md);
    cursor: pointer;
    list-style: none;
    transition: background var(--transition);
    user-select: none;
}

.accordion-header::-webkit-details-marker {
    display: none;
}

.accordion-header:hover {
    background: #f1f5f9;
}

.accordion-title {
    font-weight: 500;
    font-size: 0.8125rem;
    color: var(--text-primary);
}

.accordion-summary {
    font-size: 0.6875rem;
    font-weight: 600;
    color: var(--primary-color);
    background: rgba(59, 130, 246, 0.1);
    padding: 0.125rem 0.5rem;
    border-radius: 100px;
}

.accordion-badge {
    font-size: 0.625rem;
    font-weight: 500;
    color: var(--text-muted);
    background: var(--surface-color);
    padding: 0.125rem 0.5rem;
    border-radius: 100px;
    border: 1px solid var(--border-color);
}

.input-accordion[open] .accordion-header {
    border-radius: var(--radius-md) var(--radius-md) 0 0;
}

.accordion-content {
    padding: 0.875rem;
    background: var(--bg-color);
    border-radius: 0 0 var(--radius-md) var(--radius-md);
}

.accordion-help {
    font-size: 0.6875rem;
    color: var(--text-muted);
    margin-bottom: 0.75rem;
    line-height: 1.4;
}

/* ========== Mix Validation ========== */
.mix-validation {
    margin-top: 0.75rem;
    padding: 0.5rem 0.75rem;
    border-radius: var(--radius-sm);
    font-size: 0.75rem;
    display: none;
}

.mix-validation.visible {
    display: block;
}

.mix-validation.valid {
    background: rgba(16, 185, 129, 0.1);
    color: var(--success-color);
    border: 1px solid rgba(16, 185, 129, 0.2);
}

.mix-validation.warning {
    background: rgba(245, 158, 11, 0.1);
    color: #b45309;
    border: 1px solid rgba(245, 158, 11, 0.2);
}

.mix-validation.error {
    background: rgba(239, 68, 68, 0.1);
    color: var(--error-color);
    border: 1px solid rgba(239, 68, 68, 0.2);
}

/* ========== Input Rows ========== */
.input-row {
    margin-bottom: 0.75rem;
}

.input-row:last-child {
    margin-bottom: 0;
}

.input-row label {
    display: block;
    font-size: 0.75rem;
    font-weight: 500;
    margin-bottom: 0.375rem;
    color: var(--text-primary);
}

.input-row input[type="number"] {
    width: 100%;
    padding: 0.5rem 0.625rem;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    font-size: 0.8125rem;
    background: var(--surface-color);
    transition: border-color var(--transition), box-shadow var(--transition);
}

.input-row input[type="number"]:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.1);
}

.input-row input[type="number"].input-empty {
    border-color: var(--warning-color);
    background: rgba(245, 158, 11, 0.05);
}

.input-row input[type="number"].input-empty:focus {
    box-shadow: 0 0 0 3px rgba(245, 158, 11, 0.1);
}

/* Help Icons */
.help-icon {
    position: relative;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 14px;
    height: 14px;
    margin-left: 4px;
    font-size: 0.625rem;
    font-weight: 600;
    color: var(--text-muted);
    background: var(--surface-color);
    border: 1px solid var(--border-color);
    border-radius: 50%;
    cursor: help;
    vertical-align: middle;
    transition: all var(--transition);
}

.help-icon:hover {
    background: var(--primary-color);
    color: white;
    border-color: var(--primary-color);
}

.help-icon::after {
    content: attr(data-tooltip);
    position: absolute;
    bottom: calc(100% + 6px);
    left: 50%;
    transform: translateX(-50%);
    padding: 8px 12px;
    background: var(--surface-color);
    border: 1px solid var(--border-color);
    border-radius: 6px;
    font-size: 0.75rem;
    font-weight: 400;
    color: var(--text-primary);
    white-space: normal;
    width: max-content;
    max-width: 200px;
    opacity: 0;
    visibility: hidden;
    transition: opacity 0.15s;
    pointer-events: none;
    z-index: 1000;
    box-shadow: 0 2px 8px rgba(0,0,0,0.1);
}

.help-icon:hover::after {
    opacity: 1;
    visibility: visible;
}

/* ========== Slider Rows ========== */
.slider-row {
    display: block;
}

.slider-row label {
    margin-bottom: 0.25rem;
}

.slider-container {
    display: flex;
    align-items: center;
    gap: 0.75rem;
}

input[type="range"] {
    flex: 1;
    height: 4px;
    border-radius: 2px;
    background: var(--border-color);
    outline: none;
    -webkit-appearance: none;
    cursor: pointer;
}

input[type="range"]::-webkit-slider-thumb {
    -webkit-appearance: none;
    appearance: none;
    width: 16px;
    height: 16px;
    border-radius: 50%;
    background: var(--primary-color);
    cursor: pointer;
    transition: transform var(--transition), box-shadow var(--transition);
    box-shadow: var(--shadow-sm);
}

input[type="range"]::-webkit-slider-thumb:hover {
    transform: scale(1.1);
    box-shadow: 0 2px 8px rgba(59, 130, 246, 0.3);
}

input[type="range"]::-moz-range-thumb {
    width: 16px;
    height: 16px;
    border-radius: 50%;
    background: var(--primary-color);
    cursor: pointer;
    border: none;
}

.slider-value {
    min-width: 36px;
    text-align: right;
    font-weight: 600;
    color: var(--primary-color);
    font-size: 0.75rem;
}

/* ========== Main Content ========== */
.main-content {
    padding: 1.5rem;
    background: var(--bg-color);
    overflow-y: auto;
    min-height: 100vh;
}

/* ========== Executive Summary ========== */
.executive-summary {
    background: linear-gradient(135deg, #f0fdf4 0%, #ecfdf5 100%);
    border: 1px solid #bbf7d0;
    border-radius: var(--radius-lg);
    padding: 1.25rem;
    margin-bottom: 1rem;
}

.summary-recommendation {
    font-size: 1.125rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 1rem;
}

.summary-recommendation .highlight {
    color: var(--success-color);
}

.summary-recommendation .option-name {
    font-weight: 700;
}

.summary-costs {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 1rem;
}

.summary-cost-item {
    background: var(--surface-color);
    padding: 0.875rem;
    border-radius: var(--radius-md);
    border: 1px solid var(--border-color);
}

.summary-cost-item.cheapest {
    border-color: var(--success-color);
    background: rgba(16, 185, 129, 0.05);
}

.summary-cost-label {
    font-size: 0.6875rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-secondary);
    margin-bottom: 0.25rem;
}

.summary-cost-value {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--text-primary);
}

.summary-cost-item.cheapest .summary-cost-value {
    color: var(--success-color);
}

.summary-cost-annual {
    font-size: 0.75rem;
    color: var(--text-muted);
    margin-top: 0.125rem;
}

.summary-savings {
    margin-top: 1rem;
    padding-top: 1rem;
    border-top: 1px solid #bbf7d0;
    font-size: 0.875rem;
    color: var(--text-secondary);
}

.summary-savings strong {
    color: var(--success-color);
    font-weight: 600;
}

.summary-insight {
    margin-top: 0.75rem;
    padding: 0.75rem 1rem;
    background: var(--info-bg, #eff6ff);
    border-left: 3px solid var(--info-color, #3b82f6);
    border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
    font-size: 0.875rem;
    color: var(--text-secondary);
}

.summary-insight.warning {
    background: var(--warning-bg, #fef3c7);
    border-left-color: var(--warning-color, #f59e0b);
}

.summary-insight strong {
    color: var(--text-primary);
    font-weight: 600;
}

/* ========== Chart Section ========== */
.chart-section {
    background: var(--surface-color);
    border-radius: var(--radius-lg);
    padding: 1.25rem;
    box-shadow: var(--shadow-md);
    margin-bottom: 1rem;
}

.chart-header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    margin-bottom: 1rem;
    padding-bottom: 1rem;
    border-bottom: 1px solid var(--border-color);
    flex-wrap: wrap;
    gap: 1rem;
}

.chart-header h2 {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-primary);
    margin: 0;
}

/* ========== Chart Container ========== */
.chart-container {
    position: relative;
    height: 420px;
}

.chart-container canvas {
    max-height: 100%;
}

/* ========== Detail Sections (Collapsible) ========== */
.detail-section {
    background: var(--surface-color);
    border-radius: var(--radius-lg);
    margin-bottom: 0.75rem;
    box-shadow: var(--shadow-sm);
    overflow: hidden;
}

.detail-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0.875rem 1.25rem;
    cursor: pointer;
    list-style: none;
    transition: background var(--transition);
}

.detail-header::-webkit-details-marker {
    display: none;
}

.detail-header:hover {
    background: var(--bg-color);
}

.detail-header h3 {
    font-size: 0.875rem;
    font-weight: 600;
    margin: 0;
    color: var(--text-primary);
}

.detail-preview {
    font-size: 0.6875rem;
    font-weight: 500;
    color: var(--primary-color);
    background: rgba(59, 130, 246, 0.1);
    padding: 0.25rem 0.75rem;
    border-radius: 100px;
    transition: opacity var(--transition);
}

.detail-section[open] .detail-preview {
    opacity: 0;
}

.detail-content {
    padding: 0 1.25rem 1.25rem;
}

/* ========== Crossover Points ========== */
.crossover-container {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 0.75rem;
}

.crossover-item {
    background: var(--bg-color);
    padding: 0.875rem;
    border-radius: var(--radius-md);
    border: 1px solid var(--border-color);
}

.crossover-label {
    font-weight: 600;
    font-size: 0.8125rem;
    color: var(--text-primary);
    margin-bottom: 0.375rem;
}

.crossover-value {
    font-size: 0.9375rem;
    margin-bottom: 0.375rem;
}

.crossover-cost {
    color: var(--text-secondary);
    font-size: 0.75rem;
}

.crossover-insight {
    font-size: 0.6875rem;
    color: var(--text-secondary);
    margin-bottom: 0.375rem;
    line-height: 1.5;
}

.crossover-insight .cheaper {
    font-weight: 600;
    color: var(--success-color);
}

.crossover-you {
    font-size: 0.75rem;
    padding: 0.375rem 0.5rem;
    background: rgba(59, 130, 246, 0.08);
    border-radius: var(--radius-sm);
    color: var(--primary-color);
}

.no-crossover {
    color: var(--text-secondary);
    font-style: italic;
    font-size: 0.8125rem;
}

/* ========== Cost Structure Section ========== */
.cost-structure-section {
    background: var(--surface-color);
    border-radius: var(--radius-lg);
    padding: 1rem 1.25rem;
    margin-bottom: 0.75rem;
    box-shadow: var(--shadow-sm);
}

.cost-structure-section h3 {
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--text-primary);
    margin: 0 0 0.75rem;
}

.cost-structure-container {
    display: flex;
    flex-wrap: wrap;
    gap: 0.75rem;
}

.cost-structure-item {
    display: flex;
    flex-direction: column;
    gap: 0.125rem;
    padding: 0.5rem 0.75rem;
    background: var(--bg-color);
    border-radius: var(--radius-sm);
    border: 1px solid var(--border-color);
    min-width: 180px;
}

.cost-structure-label {
    font-size: 0.6875rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.025em;
    color: var(--text-secondary);
}

.cost-structure-formula {
    font-size: 0.8125rem;
    font-weight: 500;
    color: var(--text-primary);
    font-family: 'SF Mono', 'Consolas', 'Monaco', monospace;
}

/* ========== Rate Comparison Section ========== */
.rate-comparison-section {
    background: var(--surface-color);
    border-radius: var(--radius-lg);
    padding: 1rem 1.25rem;
    margin-bottom: 0.75rem;
    box-shadow: var(--shadow-sm);
}

.rate-comparison-section h3 {
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--text-primary);
    margin: 0 0 0.25rem;
}

.section-subtitle {
    font-size: 0.75rem;
    color: var(--text-secondary);
    margin: 0 0 0.75rem;
}

#rate-comparison-table .baseline-row {
    background: rgba(59, 130, 246, 0.05);
    border-top: 2px solid var(--border-color);
}

#rate-comparison-table .baseline-row td {
    padding-top: 0.75rem;
    padding-bottom: 0.75rem;
}

#rate-comparison-table .baseline {
    color: var(--text-muted);
    font-style: italic;
}

#rate-comparison-table .rate-note {
    font-size: 0.625rem;
    color: var(--text-muted);
    font-weight: 400;
}

#rate-comparison-table .no-data {
    color: var(--text-muted);
    font-style: italic;
    text-align: center;
    padding: 1rem;
}

/* ========== Crossover Formula ========== */
.crossover-formula {
    font-size: 0.6875rem;
    color: var(--text-secondary);
    background: rgba(59, 130, 246, 0.05);
    padding: 0.5rem;
    border-radius: var(--radius-sm);
    margin: 0.375rem 0;
    line-height: 1.6;
}

.crossover-formula .formula-label {
    font-weight: 600;
    color: var(--text-primary);
}

.crossover-formula .formula-calc {
    display: block;
    font-family: 'SF Mono', 'Consolas', 'Monaco', monospace;
    color: var(--primary-color);
    margin-top: 0.25rem;
}

/* ========== Data Table ========== */
.table-wrapper {
    overflow-x: auto;
}

table {
    width: 100%;
    border-collapse: collapse;
    font-size: 0.75rem;
}

thead th {
    background: var(--bg-color);
    padding: 0.625rem 0.75rem;
    text-align: left;
    font-weight: 600;
    font-size: 0.6875rem;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.025em;
    border-bottom: 1px solid var(--border-color);
}

tbody td {
    padding: 0.625rem 0.75rem;
    border-bottom: 1px solid var(--border-color);
    vertical-align: top;
}

tbody tr:hover {
    background: var(--bg-color);
}

tfoot td {
    padding: 0.625rem 0.75rem;
    font-weight: 600;
    border-top: 2px solid var(--border-color);
    background: var(--bg-color);
}

.formula {
    color: var(--text-muted);
    font-size: 0.625rem;
    font-style: italic;
    margin-top: 0.125rem;
}

.cost-value {
    font-weight: 600;
    color: var(--text-primary);
}

.diff-positive {
    color: var(--error-color);
}

.diff-negative {
    color: var(--success-color);
}

/* Table Group Headers */
.group-header td {
    background: var(--bg-color);
    font-weight: 600;
    font-size: 0.6875rem;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-secondary);
    padding: 0.5rem 0.75rem;
    border-bottom: 1px solid var(--border-color);
}

.group-header .group-note {
    font-weight: 400;
    text-transform: none;
    letter-spacing: normal;
    color: var(--text-muted);
    font-style: italic;
}

/* ========== Responsive ========== */
@media (max-width: 1024px) {
    .app-layout {
        grid-template-columns: 1fr;
    }

    .sidebar {
        position: relative;
        height: auto;
        max-height: none;
        border-right: none;
        border-bottom: 1px solid var(--border-color);
    }

    .sidebar-content {
        max-height: 50vh;
    }

    .main-content {
        min-height: auto;
    }

    .chart-container {
        height: 350px;
    }

    .chart-header {
        flex-direction: column;
        align-items: flex-start;
    }
}

@media (max-width: 640px) {
    .main-content {
        padding: 1rem;
    }

    .chart-container {
        height: 280px;
    }

    .crossover-container {
        grid-template-columns: 1fr;
    }

    table {
        font-size: 0.6875rem;
    }

    thead th,
    tbody td,
    tfoot td {
        padding: 0.5rem;
    }
}