:root {
    --bg: #0f172a;
    --surface: #1e293b;
    --surface-hover: #334155;
    --text: #f8fafc;
    --text-muted: #a3b5c7;
    --accent: #38bdf8;
    --accent-hover: #0ea5e9;
    --danger: #ef4444;
    --warning: #f59e0b;
    --success: #22c55e;
    --border: #334155;
    --radius: 12px;
    --shadow: 0 4px 6px -1px rgb(0 0 0 / 0.3);
    --tooltip-bg: #1e293b;
    --tooltip-text: #f8fafc;
    --chart-grid: rgba(51, 65, 85, 0.5);
    --chart-text: #a3b5c7;
    --row-hover: rgba(255, 255, 255, 0.02);
    --td-border: rgba(51, 65, 85, 0.5);
}

[data-theme="light"] {
    --bg: #f8fafc;
    --surface: #ffffff;
    --surface-hover: #f1f5f9;
    --text: #0f172a;
    --text-muted: #64748b;
    --accent: #0284c7;
    --accent-hover: #0369a1;
    --danger: #dc2626;
    --warning: #d97706;
    --success: #16a34a;
    --border: #e2e8f0;
    --shadow: 0 4px 6px -1px rgb(0 0 0 / 0.1);
    --tooltip-bg: #1e293b;
    --tooltip-text: #f8fafc;
    --chart-grid: rgba(148, 163, 184, 0.3);
    --chart-text: #64748b;
    --row-hover: rgba(0, 0, 0, 0.02);
    --td-border: rgba(226, 232, 240, 0.8);
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'PingFang SC', 'Microsoft YaHei', 'Hiragino Sans GB', 'Noto Sans CJK SC', sans-serif;
    background: var(--bg);
    color: var(--text);
    line-height: 1.6;
    min-height: 100vh;
    transition: background-color 0.3s, color 0.3s;
}

.container {
    max-width: 900px;
    margin: 0 auto;
    padding: 2rem 1rem;
}

header {
    text-align: center;
    margin-bottom: 2.5rem;
}

.header-top {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 1rem;
    position: relative;
}

header h1 {
    font-size: 2.5rem;
    font-weight: 800;
    background: linear-gradient(135deg, var(--accent), #818cf8);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    margin-bottom: 0.5rem;
}

.subtitle {
    color: var(--text-muted);
    font-size: 1.05rem;
}

.header-controls {
    position: absolute;
    right: 0;
    top: 50%;
    transform: translateY(-50%);
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.lang-selector {
    display: flex;
    align-items: center;
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: 20px;
    overflow: hidden;
    box-shadow: var(--shadow);
}

.lang-btn {
    background: transparent;
    border: none;
    color: var(--text-muted);
    font-size: 0.8rem;
    font-weight: 600;
    padding: 0.4rem 0.7rem;
    cursor: pointer;
    transition: all 0.2s;
    font-family: inherit;
}

.lang-btn:hover {
    color: var(--text);
}

.lang-btn.active {
    background: var(--accent);
    color: white;
}

.theme-toggle {
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: 50%;
    width: 40px;
    height: 40px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    font-size: 1.1rem;
    transition: all 0.2s;
    box-shadow: var(--shadow);
}

.theme-toggle:hover {
    transform: scale(1.1);
    border-color: var(--accent);
}

.inputs {
    display: grid;
    grid-template-columns: 1fr;
    gap: 1.25rem;
    background: var(--surface);
    padding: 1.5rem;
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    margin-bottom: 2rem;
    transition: background-color 0.3s;
}

.input-section {
    grid-column: 1 / -1;
}

.section-header {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    margin-bottom: 0.75rem;
}

.step-badge {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 24px;
    height: 24px;
    border-radius: 50%;
    background: var(--accent);
    color: white;
    font-size: 0.75rem;
    font-weight: 700;
    flex-shrink: 0;
}

.section-label {
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--text);
}

.section-inputs {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 1.25rem;
}

.input-group {
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}

.input-group label {
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--text-muted);
    letter-spacing: 0.01em;
    display: flex;
    align-items: center;
    gap: 0.35rem;
}

.input-group label .optional {
    font-weight: 400;
    opacity: 0.7;
}

.tooltip {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 16px;
    height: 16px;
    border-radius: 50%;
    background: var(--border);
    color: var(--text-muted);
    font-size: 0.7rem;
    font-weight: 700;
    cursor: help;
    position: relative;
    transition: background-color 0.2s, color 0.2s;
}

.tooltip:hover {
    background: var(--accent);
    color: white;
}

.tooltip::after {
    content: attr(data-tooltip);
    position: absolute;
    bottom: calc(100% + 8px);
    left: 50%;
    transform: translateX(-50%);
    background: var(--tooltip-bg);
    color: var(--tooltip-text);
    padding: 0.5rem 0.75rem;
    border-radius: 8px;
    font-size: 0.8rem;
    font-weight: 400;
    white-space: nowrap;
    opacity: 0;
    visibility: hidden;
    transition: opacity 0.2s, visibility 0.2s;
    pointer-events: none;
    z-index: 100;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
    letter-spacing: normal;
}

.tooltip::before {
    content: '';
    position: absolute;
    bottom: calc(100% + 3px);
    left: 50%;
    transform: translateX(-50%);
    border: 5px solid transparent;
    border-top-color: var(--tooltip-bg);
    opacity: 0;
    visibility: hidden;
    transition: opacity 0.2s, visibility 0.2s;
    pointer-events: none;
    z-index: 100;
}

.tooltip:hover::after,
.tooltip:hover::before {
    opacity: 1;
    visibility: visible;
}

.input-group input {
    padding: 0.75rem 1rem;
    border: 1px solid var(--border);
    border-radius: 8px;
    background: var(--bg);
    color: var(--text);
    font-size: 1rem;
    transition: border-color 0.2s, box-shadow 0.2s, background-color 0.3s, color 0.3s;
}

.input-group input:focus {
    outline: none;
    border-color: var(--accent);
    box-shadow: 0 0 0 3px rgba(56, 189, 248, 0.15);
}

.input-group input.error {
    border-color: var(--danger);
    box-shadow: 0 0 0 3px rgba(239, 68, 68, 0.15);
}

.error-message {
    color: var(--danger);
    font-size: 0.8rem;
    min-height: 1.2em;
    display: none;
}

.error-message.visible {
    display: block;
}

.input-hint {
    color: var(--text-muted);
    font-size: 0.8rem;
    opacity: 0.8;
}

.risk-slider-group {
    grid-column: 1 / -1;
}

.btn-primary {
    grid-column: 1 / -1;
    padding: 0.875rem 1.5rem;
    background: linear-gradient(135deg, var(--accent), var(--accent-hover));
    color: white;
    border: none;
    border-radius: 8px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: transform 0.15s, box-shadow 0.15s;
}

.btn-primary:hover {
    transform: translateY(-1px);
    box-shadow: 0 8px 16px -4px rgba(56, 189, 248, 0.3);
}

.btn-primary:active {
    transform: translateY(0);
}

.btn-secondary {
    grid-column: 1 / -1;
    padding: 0.75rem 1.5rem;
    background: transparent;
    color: var(--accent);
    border: 1px solid var(--border);
    border-radius: 8px;
    font-size: 0.95rem;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.15s;
}

.btn-secondary:hover {
    border-color: var(--accent);
    background: rgba(56, 189, 248, 0.05);
}

.advanced-settings {
    margin-top: 0.5rem;
}

.advanced-settings summary {
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--text-muted);
    cursor: pointer;
    padding: 0.5rem 0;
    list-style: none;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.advanced-settings summary::-webkit-details-marker {
    display: none;
}

.advanced-settings summary::before {
    content: '▸';
    font-size: 0.8rem;
    transition: transform 0.2s;
}

.advanced-settings[open] summary::before {
    content: '▾';
}

.advanced-settings[open] summary {
    color: var(--text);
    margin-bottom: 0.75rem;
}

.results-empty .chart-placeholder {
    display: flex;
}

.results-empty canvas {
    display: none !important;
}

.results-empty .skeleton-row {
    display: table-row;
}

.results-empty .summary-card .value {
    color: var(--text-muted);
}

.results:not(.results-empty) .skeleton-row {
    display: none;
}

.chart-placeholder {
    display: none;
    height: 100%;
    min-height: 280px;
    align-items: center;
    justify-content: center;
    flex-direction: column;
    gap: 0.75rem;
    color: var(--text-muted);
    text-align: center;
    padding: 2rem;
}

.chart-icon {
    font-size: 2.5rem;
    opacity: 0.5;
}

.chart-placeholder p {
    font-size: 0.95rem;
    max-width: 280px;
    line-height: 1.5;
}

.skeleton-row {
    height: 40px;
}

.skeleton-row td {
    padding: 0;
    border-bottom: 1px solid var(--td-border);
}

.skeleton-row td::after {
    content: '';
    display: block;
    height: 24px;
    margin: 8px 1rem;
    border-radius: 4px;
    background: linear-gradient(90deg, var(--surface) 25%, var(--surface-hover) 50%, var(--surface) 75%);
    background-size: 200% 100%;
    animation: skeleton-pulse 1.5s infinite;
}

@keyframes skeleton-pulse {
    0% { background-position: 200% 0; }
    100% { background-position: -200% 0; }
}

@keyframes flash-highlight {
    0% { box-shadow: 0 0 0 0 rgba(56, 189, 248, 0.4); }
    50% { box-shadow: 0 0 0 12px rgba(56, 189, 248, 0); }
    100% { box-shadow: 0 0 0 0 rgba(56, 189, 248, 0); }
}

.results-flash {
    animation: flash-highlight 1s ease-out;
}

.risk-summary {
    display: flex;
    gap: 1rem;
    margin-bottom: 1.5rem;
    flex-wrap: wrap;
}

.summary-card {
    background: var(--surface);
    padding: 1.25rem 1.5rem;
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    flex: 1;
    min-width: 150px;
    display: flex;
    flex-direction: column;
    gap: 0.25rem;
    transition: background-color 0.3s;
}

.summary-card .label {
    font-size: 0.75rem;
    letter-spacing: 0.02em;
    color: var(--text-muted);
    font-weight: 600;
}

.summary-card .value {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--accent);
}

.chart-container {
    background: var(--surface);
    padding: 1.5rem;
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    margin-bottom: 1.5rem;
    min-height: 320px;
    position: relative;
    transition: background-color 0.3s;
}

.table-container {
    background: var(--surface);
    padding: 1.5rem;
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    overflow-x: auto;
    transition: background-color 0.3s;
}

table {
    width: 100%;
    border-collapse: collapse;
    font-size: 0.95rem;
}

th, td {
    padding: 0.875rem 1rem;
    text-align: left;
}

th {
    font-size: 0.75rem;
    letter-spacing: 0.02em;
    color: var(--text-muted);
    font-weight: 600;
    border-bottom: 1px solid var(--border);
}

td {
    border-bottom: 1px solid var(--td-border);
}

tr:last-child td {
    border-bottom: none;
}

tr:hover td {
    background: var(--row-hover);
}

.recommended-row {
    background: rgba(56, 189, 248, 0.08) !important;
    border-left: 3px solid var(--accent);
}

.recommended-row td:first-child {
    position: relative;
}

.recommended-badge {
    display: inline-block;
    background: var(--accent);
    color: var(--bg);
    font-size: 0.65rem;
    font-weight: 700;
    letter-spacing: 0.02em;
    padding: 0.15rem 0.4rem;
    border-radius: 4px;
    margin-left: 0.5rem;
    vertical-align: middle;
}

.risk-low { color: var(--success); }
.risk-med { color: var(--warning); }
.risk-high { color: var(--danger); }

.risk-label {
    font-size: 0.75rem;
    opacity: 0.85;
    margin-left: 0.35rem;
    font-weight: 500;
}

.copy-btn {
    background: transparent;
    border: 1px solid var(--border);
    color: var(--text-muted);
    padding: 0.35rem 0.75rem;
    border-radius: 6px;
    font-size: 0.8rem;
    cursor: pointer;
    transition: all 0.15s;
    white-space: nowrap;
}

.copy-btn:hover {
    border-color: var(--accent);
    color: var(--accent);
}

.copy-btn.copied {
    border-color: var(--success);
    color: var(--success);
}

/* Education section */
.edu-section {
    background: var(--surface);
    border-radius: var(--radius);
    border-left: 4px solid var(--accent);
    box-shadow: var(--shadow);
    margin-bottom: 2rem;
    transition: background-color 0.3s;
    overflow: hidden;
}

.edu-section summary {
    padding: 1rem 1.25rem;
    cursor: pointer;
    list-style: none;
    display: flex;
    align-items: center;
    gap: 0.5rem;
    font-weight: 600;
    color: var(--text);
    font-size: 1rem;
    transition: background-color 0.2s;
}

.edu-section summary:hover {
    background: var(--row-hover);
}

.edu-section summary::-webkit-details-marker {
    display: none;
}

.edu-icon {
    font-size: 1.25rem;
    line-height: 1;
}

.edu-content {
    padding: 0 1.25rem 1.25rem;
    display: flex;
    flex-direction: column;
    gap: 1.25rem;
}

.edu-lead {
    font-size: 1.05rem;
    font-weight: 600;
    color: var(--text);
    line-height: 1.5;
    margin: 0;
}

.edu-analogy,
.edu-formula,
.edu-when {
    background: var(--bg);
    border-radius: 8px;
    padding: 1rem;
    transition: background-color 0.3s;
}

.edu-analogy strong,
.edu-formula strong,
.edu-when strong {
    display: block;
    margin-bottom: 0.5rem;
    color: var(--accent);
    font-size: 0.9rem;
}

.edu-analogy p,
.edu-when p,
.edu-when li {
    color: var(--text-muted);
    font-size: 0.9rem;
    line-height: 1.6;
    margin: 0;
}

.edu-when ul {
    margin: 0;
    padding-left: 1.25rem;
}

.edu-when li {
    margin-bottom: 0.35rem;
}

.edu-when li:last-child {
    margin-bottom: 0;
}

.formula-flow {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.75rem;
    flex-wrap: wrap;
    padding: 0.5rem 0;
}

.formula-step {
    background: var(--surface);
    color: var(--text);
    padding: 0.5rem 0.75rem;
    border-radius: 6px;
    font-size: 0.85rem;
    font-weight: 600;
    border: 1px solid var(--border);
    transition: background-color 0.3s, color 0.3s;
}

.formula-arrow {
    color: var(--accent);
    font-size: 1.1rem;
    font-weight: 700;
}

/* Flow diagram (empty state) */
.flow-diagram {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    flex-wrap: wrap;
    margin-bottom: 0.5rem;
}

.flow-step {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 0.25rem;
    background: var(--bg);
    padding: 0.75rem 1rem;
    border-radius: 8px;
    border: 1px solid var(--border);
    min-width: 90px;
    transition: background-color 0.3s;
}

.flow-icon {
    font-size: 1.5rem;
    line-height: 1;
}

.flow-label {
    font-size: 0.8rem;
    font-weight: 600;
    color: var(--text);
}

.flow-example {
    font-size: 0.75rem;
    color: var(--text-muted);
}

.flow-arrow {
    color: var(--accent);
    font-size: 1.25rem;
    font-weight: 700;
}

/* Results context */
.results-context {
    background: var(--surface);
    padding: 1rem 1.25rem;
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    margin-bottom: 1.5rem;
    border-left: 4px solid var(--warning);
    transition: background-color 0.3s;
}

.results-context p {
    margin: 0;
    color: var(--text-muted);
    font-size: 0.9rem;
    line-height: 1.6;
}

.results-context strong {
    color: var(--text);
}

.recommended-context {
    background: var(--surface);
    padding: 1rem 1.25rem;
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    margin-top: 1.5rem;
    display: flex;
    align-items: center;
    gap: 0.75rem;
    flex-wrap: wrap;
    transition: background-color 0.3s;
}

.recommended-context .recommended-badge {
    margin-left: 0;
    flex-shrink: 0;
}

.recommended-context span:last-child {
    color: var(--text-muted);
    font-size: 0.9rem;
    line-height: 1.5;
}

/* Educational inline hints */
.edu-hint {
    color: var(--accent);
    opacity: 0.9;
    font-size: 0.8rem;
    line-height: 1.5;
}

/* Empty state visibility rules */
.results-empty .results-context,
.results-empty .recommended-context {
    display: none;
}

footer {
    text-align: center;
    margin-top: 3rem;
    padding-top: 2rem;
    border-top: 1px solid var(--border);
    color: var(--text-muted);
    font-size: 0.875rem;
}

@media (max-width: 640px) {
    header h1 {
        font-size: 2rem;
    }

    .header-top {
        padding: 0 3rem;
    }

    .header-controls {
        right: 0;
    }

    .lang-btn {
        padding: 0.35rem 0.5rem;
        font-size: 0.75rem;
    }

    .theme-toggle {
        width: 36px;
        height: 36px;
        font-size: 1rem;
    }

    .section-inputs {
        grid-template-columns: 1fr;
    }

    .chart-container {
        min-height: 260px;
        padding: 1rem;
    }

    .chart-placeholder {
        min-height: 220px;
    }

    th, td {
        padding: 0.625rem 0.75rem;
        font-size: 0.875rem;
    }

    .tooltip::after {
        white-space: normal;
        width: 200px;
        left: auto;
        right: 0;
        transform: none;
    }

    .tooltip::before {
        left: auto;
        right: 6px;
        transform: none;
    }

    .flow-diagram {
        flex-direction: column;
        gap: 0.5rem;
    }

    .flow-arrow {
        transform: rotate(90deg);
    }

    .flow-step {
        min-width: 140px;
        width: 100%;
        max-width: 200px;
    }

    .formula-flow {
        flex-direction: column;
        gap: 0.5rem;
    }

    .formula-arrow {
        transform: rotate(90deg);
    }

    .edu-content {
        padding: 0 1rem 1rem;
    }

    .results-context,
    .recommended-context {
        padding: 0.875rem 1rem;
    }
}