/* ============================================================
   SWISS CLEAN MINIMALIST DESIGN SYSTEM — HVAC DUCT CALCULATOR
   ============================================================ */

:root {
    --bg-canvas: #ffffff;
    --bg-surface: #fafafa;
    --bg-subtle: #f4f4f5;
    --text-primary: #09090b;
    --text-muted: #71717a;
    --text-subtle: #a1a1aa;
    --border-color: #e4e4e7;
    --border-strong: #d4d4d8;
    --accent-black: #000000;
    --accent-white: #ffffff;
    --color-success: #16a34a;
    --color-success-bg: #f0fdf4;
    --color-warning: #d97706;
    --color-warning-bg: #fffbeb;
    --color-danger: #dc2626;
    --color-danger-bg: #fef2f2;
    --radius-sm: 4px;
    --radius-md: 6px;
    --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    --font-mono: 'JetBrains Mono', ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
}

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

html {
    scroll-behavior: smooth;
    background-color: var(--bg-canvas);
    color: var(--text-primary);
    font-family: var(--font-sans);
    line-height: 1.5;
    -webkit-font-smoothing: antialiased;
    overflow-x: hidden;
    width: 100%;
    max-width: 100%;
}

body {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    background-color: var(--bg-canvas);
    color: var(--text-primary);
    overflow-x: hidden;
    width: 100%;
    max-width: 100%;
}

/* ================= HEADER & NAV ================= */
.site-header {
    border-bottom: 1px solid var(--border-color);
    background-color: var(--bg-canvas);
    position: sticky;
    top: 0;
    z-index: 40;
}

.header-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 1.5rem;
    height: 4rem;
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.brand-block {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    text-decoration: none;
    color: var(--text-primary);
}

.brand-icon {
    width: 2.25rem;
    height: 2.25rem;
    background-color: var(--accent-black);
    color: var(--accent-white);
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: var(--radius-sm);
    font-size: 1.1rem;
    font-weight: 700;
}

.brand-title {
    font-size: 1.125rem;
    font-weight: 800;
    letter-spacing: -0.03em;
    line-height: 1.2;
}

.brand-subtitle {
    font-size: 0.7rem;
    color: var(--text-muted);
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.header-nav {
    display: flex;
    align-items: center;
    gap: 1.25rem;
}

.nav-link {
    font-size: 0.875rem;
    font-weight: 500;
    color: var(--text-muted);
    text-decoration: none;
    transition: color 0.15s ease;
}

.nav-link:hover {
    color: var(--text-primary);
}

.btn-header-cta {
    background-color: var(--accent-black);
    color: var(--accent-white);
    font-size: 0.8125rem;
    font-weight: 600;
    padding: 0.5rem 0.875rem;
    border-radius: var(--radius-sm);
    text-decoration: none;
    border: 1px solid var(--accent-black);
    cursor: pointer;
    transition: background-color 0.15s ease;
    box-sizing: border-box;
    white-space: nowrap;
}

.btn-header-cta:hover {
    background-color: #27272a;
}

@media (max-width: 640px) {
    .header-nav .nav-link {
        display: none;
    }
    .header-container {
        padding: 0.75rem 1rem;
    }
    .brand-title {
        font-size: 1rem;
    }
    .header-nav {
        gap: 0.5rem;
    }
}

/* ================= MAIN CONTAINER ================= */
.main-wrapper {
    flex: 1;
    max-width: 1200px;
    width: 100%;
    margin: 0 auto;
    padding: 2.5rem 1.5rem;
}

.hero-section {
    margin-bottom: 2.5rem;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 2rem;
}

.hero-badge {
    display: inline-flex;
    align-items: center;
    gap: 0.375rem;
    font-size: 0.75rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    background-color: var(--bg-surface);
    color: var(--text-muted);
    border: 1px solid var(--border-color);
    padding: 0.25rem 0.625rem;
    border-radius: var(--radius-sm);
    margin-bottom: 1rem;
}

.hero-title {
    font-size: 2.25rem;
    font-weight: 800;
    letter-spacing: -0.03em;
    line-height: 1.2;
    margin-bottom: 0.75rem;
}

.hero-lead {
    font-size: 1.0625rem;
    color: var(--text-muted);
    max-width: 780px;
    line-height: 1.6;
}

/* ================= GRID LAYOUT ================= */
.calculator-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: 2rem;
    margin-bottom: 3rem;
}

@media (min-width: 992px) {
    .calculator-grid {
        grid-template-columns: 1.15fr 0.85fr;
    }
}

.calc-panel {
    background-color: var(--bg-surface);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 1.75rem;
}

.calc-panel-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding-bottom: 1.25rem;
    margin-bottom: 1.5rem;
    border-bottom: 1px solid var(--border-color);
}

.calc-panel-title {
    font-size: 1.125rem;
    font-weight: 700;
    letter-spacing: -0.02em;
}

/* Mode Tabs */
.tab-group {
    display: flex;
    background-color: var(--bg-canvas);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    padding: 0.25rem;
    margin-bottom: 1.75rem;
    gap: 0.25rem;
}

.tab-btn {
    flex: 1;
    background: transparent;
    border: none;
    padding: 0.5rem 0.75rem;
    font-size: 0.8125rem;
    font-weight: 600;
    color: var(--text-muted);
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: all 0.15s ease;
    text-align: center;
}

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

.tab-btn:hover:not(.active) {
    color: var(--text-primary);
    background-color: var(--bg-subtle);
}

/* Form Controls */
.form-group {
    margin-bottom: 1.25rem;
}

.form-label-row {
    display: flex;
    justify-content: space-between;
    align-items: baseline;
    margin-bottom: 0.5rem;
}

.form-label {
    font-size: 0.8125rem;
    font-weight: 600;
    color: var(--text-primary);
}

.form-hint {
    font-size: 0.75rem;
    color: var(--text-muted);
    font-family: var(--font-mono);
}

.input-container {
    position: relative;
    display: flex;
    align-items: center;
}

.input-field {
    width: 100%;
    background-color: var(--bg-canvas);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    padding: 0.625rem 0.875rem;
    font-size: 0.9375rem;
    font-family: var(--font-mono);
    color: var(--text-primary);
    outline: none;
    transition: border-color 0.15s ease;
}

.input-field:focus {
    border-color: var(--accent-black);
}

.input-unit {
    position: absolute;
    right: 0.875rem;
    font-size: 0.75rem;
    font-weight: 600;
    color: var(--text-muted);
    font-family: var(--font-mono);
    pointer-events: none;
}

.select-field {
    width: 100%;
    background-color: var(--bg-canvas);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    padding: 0.625rem 0.875rem;
    font-size: 0.875rem;
    color: var(--text-primary);
    outline: none;
    cursor: pointer;
    transition: border-color 0.15s ease;
}

.select-field:focus {
    border-color: var(--accent-black);
}

/* Slider Controls */
.slider-row {
    display: flex;
    align-items: center;
    gap: 1rem;
    margin-top: 0.5rem;
}

.range-slider {
    flex: 1;
    accent-color: var(--accent-black);
    cursor: pointer;
}

/* Action Buttons */
.button-row {
    display: flex;
    gap: 0.75rem;
    margin-top: 1.75rem;
    padding-top: 1.25rem;
    border-top: 1px solid var(--border-color);
}

.btn-primary {
    flex: 2;
    background-color: var(--accent-black);
    color: var(--accent-white);
    border: 1px solid var(--accent-black);
    padding: 0.75rem 1.25rem;
    border-radius: var(--radius-sm);
    font-size: 0.875rem;
    font-weight: 600;
    cursor: pointer;
    transition: background-color 0.15s ease;
    text-align: center;
}

.btn-primary:hover {
    background-color: #27272a;
}

.btn-secondary {
    flex: 1;
    background-color: var(--bg-canvas);
    color: var(--text-primary);
    border: 1px solid var(--border-color);
    padding: 0.75rem 1rem;
    border-radius: var(--radius-sm);
    font-size: 0.875rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.15s ease;
    text-align: center;
}

.btn-secondary:hover {
    background-color: var(--bg-subtle);
    border-color: var(--border-strong);
}

/* ================= RESULTS PANEL ================= */
.results-card {
    background-color: var(--bg-surface);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 1.75rem;
    display: flex;
    flex-direction: column;
}

.results-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 1.5rem;
    padding-bottom: 1rem;
    border-bottom: 1px solid var(--border-color);
}

.results-header-title {
    font-size: 1.125rem;
    font-weight: 700;
    letter-spacing: -0.02em;
}

.unit-badge {
    font-size: 0.6875rem;
    font-weight: 700;
    font-family: var(--font-mono);
    text-transform: uppercase;
    background-color: var(--bg-canvas);
    border: 1px solid var(--border-color);
    padding: 0.25rem 0.5rem;
    border-radius: var(--radius-sm);
}

/* Hero Metric Display */
.metric-hero {
    background-color: var(--bg-canvas);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    padding: 1.25rem;
    margin-bottom: 1.25rem;
    text-align: center;
}

.metric-hero-label {
    font-size: 0.75rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-muted);
    margin-bottom: 0.25rem;
}

.metric-hero-value {
    font-size: 2.25rem;
    font-weight: 800;
    letter-spacing: -0.03em;
    font-family: var(--font-mono);
    color: var(--text-primary);
}

.metric-hero-sub {
    font-size: 0.8125rem;
    color: var(--text-muted);
    margin-top: 0.25rem;
}

/* Secondary Metrics Grid */
.metrics-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 0.75rem;
    margin-bottom: 1.25rem;
}

.metric-cell {
    background-color: var(--bg-canvas);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    padding: 0.875rem;
}

.metric-cell-label {
    font-size: 0.7rem;
    font-weight: 600;
    text-transform: uppercase;
    color: var(--text-muted);
    margin-bottom: 0.25rem;
}

.metric-cell-value {
    font-size: 1.125rem;
    font-weight: 700;
    font-family: var(--font-mono);
    color: var(--text-primary);
}

/* Velocity Status Indicator */
.status-indicator {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    padding: 0.75rem 1rem;
    border-radius: var(--radius-sm);
    margin-bottom: 1.25rem;
    font-size: 0.8125rem;
    font-weight: 500;
}

.status-indicator.optimal {
    background-color: var(--color-success-bg);
    border: 1px solid #bbf7d0;
    color: #14532d;
}

.status-indicator.warning {
    background-color: var(--color-warning-bg);
    border: 1px solid #fde68a;
    color: #78350f;
}

.status-indicator.danger {
    background-color: var(--color-danger-bg);
    border: 1px solid #fecaca;
    color: #7f1d1d;
}

.status-dot {
    width: 0.625rem;
    height: 0.625rem;
    border-radius: 50%;
    flex-shrink: 0;
}

.optimal .status-dot { background-color: var(--color-success); }
.warning .status-dot { background-color: var(--color-warning); }
.danger .status-dot { background-color: var(--color-danger); }

/* SVG Diagram Box */
.diagram-box {
    background-color: var(--bg-canvas);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    padding: 1rem;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    min-height: 140px;
    margin-bottom: 1.25rem;
}

.diagram-caption {
    font-size: 0.75rem;
    color: var(--text-muted);
    font-family: var(--font-mono);
    margin-top: 0.5rem;
}

/* Quick Copy Export Bar */
.copy-report-btn {
    width: 100%;
    background-color: var(--bg-canvas);
    border: 1px solid var(--border-color);
    padding: 0.625rem;
    border-radius: var(--radius-sm);
    font-size: 0.8125rem;
    font-weight: 600;
    color: var(--text-primary);
    cursor: pointer;
    transition: background-color 0.15s ease;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
}

.copy-report-btn:hover {
    background-color: var(--bg-subtle);
}

/* ================= METHODOLOGY & EDUCATION SECTION ================= */
.education-section {
    border-top: 1px solid var(--border-color);
    padding-top: 3rem;
    margin-top: 2rem;
}

.section-eyebrow {
    font-size: 0.75rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    color: var(--text-muted);
    margin-bottom: 0.5rem;
}

.section-heading {
    font-size: 1.75rem;
    font-weight: 800;
    letter-spacing: -0.03em;
    margin-bottom: 1.5rem;
}

.methodology-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: 1.5rem;
    margin-bottom: 2.5rem;
}

@media (min-width: 768px) {
    .methodology-grid {
        grid-template-columns: repeat(3, 1fr);
    }
}

.method-card {
    background-color: var(--bg-surface);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 1.5rem;
}

.method-card-title {
    font-size: 1rem;
    font-weight: 700;
    margin-bottom: 0.75rem;
    letter-spacing: -0.02em;
}

.method-card-text {
    font-size: 0.875rem;
    color: var(--text-muted);
    line-height: 1.6;
}

.formula-display {
    background-color: var(--bg-canvas);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    padding: 0.75rem;
    margin-top: 0.75rem;
    font-family: var(--font-mono);
    font-size: 0.8125rem;
    color: var(--text-primary);
    overflow-x: auto;
}

/* Reference Table */
.reference-card {
    background-color: var(--bg-surface);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 1.75rem;
    margin-bottom: 2.5rem;
}

.table-responsive-wrapper {
    width: 100%;
    max-width: 100%;
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
}

.ref-table {
    width: 100%;
    border-collapse: collapse;
    font-size: 0.875rem;
    margin-top: 1rem;
}

.ref-table th, .ref-table td {
    padding: 0.75rem 1rem;
    text-align: left;
    border-bottom: 1px solid var(--border-color);
}

.ref-table th {
    font-size: 0.75rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-muted);
    background-color: var(--bg-canvas);
}

.ref-table tr:hover td {
    background-color: var(--bg-canvas);
}

/* ================= FOOTER ================= */
.site-footer {
    border-top: 1px solid var(--border-color);
    background-color: var(--bg-surface);
    padding: 3rem 1.5rem 2rem;
    font-size: 0.875rem;
    color: var(--text-muted);
}

.footer-container {
    max-width: 1200px;
    margin: 0 auto;
}

.footer-top {
    display: flex;
    flex-direction: column;
    gap: 2rem;
    padding-bottom: 2rem;
    border-bottom: 1px solid var(--border-color);
}

@media (min-width: 768px) {
    .footer-top {
        flex-direction: row;
        justify-content: space-between;
        align-items: flex-start;
    }
}

.footer-brand {
    max-width: 360px;
}

.footer-brand-name {
    font-size: 1rem;
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: 0.5rem;
}

.footer-desc {
    font-size: 0.8125rem;
    line-height: 1.6;
}

.footer-links-group {
    display: flex;
    flex-wrap: wrap;
    gap: 1.5rem;
}

.footer-link {
    color: var(--text-muted);
    text-decoration: none;
    font-size: 0.8125rem;
    font-weight: 500;
    transition: color 0.15s ease;
}

.footer-link:hover {
    color: var(--text-primary);
}

.footer-bottom {
    padding-top: 1.5rem;
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
    font-size: 0.75rem;
    color: var(--text-subtle);
}

@media (min-width: 768px) {
    .footer-bottom {
        flex-direction: row;
        justify-content: space-between;
        align-items: center;
    }
}

/* Value-Driven Donation System (Buy Me a Coffee) */
.support-widget-float {
    position: fixed;
    bottom: 1.5rem;
    right: 1.5rem;
    z-index: 50;
}

.support-widget-btn {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    background-color: #f59e0b;
    color: #09090b;
    font-size: 0.75rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    padding: 0.75rem 1.125rem;
    border-radius: 9999px;
    text-decoration: none;
    border: 1px solid #d97706;
    box-shadow: 0 4px 12px rgba(245, 158, 11, 0.25);
    transition: transform 0.15s ease, background-color 0.15s ease;
}

.support-widget-btn:hover {
    transform: translateY(-2px);
    background-color: #fbbf24;
}

/* ================= MODAL & DIALOG SYSTEM ================= */
.modal-overlay {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: rgba(9, 9, 11, 0.6);
    display: none;
    align-items: center;
    justify-content: center;
    padding: 1.5rem;
    z-index: 100;
}

.modal-overlay.open {
    display: flex;
}

.modal-window {
    background-color: var(--bg-canvas);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    max-width: 520px;
    width: 100%;
    box-shadow: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
    overflow: hidden;
}

.modal-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 1.25rem 1.5rem;
    border-bottom: 1px solid var(--border-color);
}

.modal-title {
    font-size: 1.125rem;
    font-weight: 700;
    letter-spacing: -0.02em;
}

.modal-close-btn {
    background: transparent;
    border: none;
    font-size: 1.25rem;
    color: var(--text-muted);
    cursor: pointer;
    padding: 0.25rem;
    line-height: 1;
}

.modal-close-btn:hover {
    color: var(--text-primary);
}

.modal-tabs {
    display: flex;
    background-color: var(--bg-surface);
    border-bottom: 1px solid var(--border-color);
}

.modal-tab-btn {
    flex: 1;
    background: transparent;
    border: none;
    border-bottom: 2px solid transparent;
    padding: 0.75rem 0.5rem;
    font-size: 0.75rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-muted);
    cursor: pointer;
}

.modal-tab-btn.active {
    color: var(--accent-black);
    border-bottom-color: var(--accent-black);
}

.modal-body {
    padding: 1.5rem;
}

.modal-form {
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

.modal-btn-submit {
    background-color: var(--accent-black);
    color: var(--accent-white);
    border: 1px solid var(--accent-black);
    padding: 0.75rem;
    border-radius: var(--radius-sm);
    font-size: 0.875rem;
    font-weight: 600;
    cursor: pointer;
    transition: background-color 0.15s ease;
    margin-top: 0.5rem;
}

.modal-btn-submit:hover {
    background-color: #27272a;
}

.form-feedback {
    display: none;
    padding: 0.75rem;
    border-radius: var(--radius-sm);
    font-size: 0.8125rem;
    line-height: 1.4;
    margin-top: 0.5rem;
}

.form-feedback.success {
    display: block;
    background-color: var(--color-success-bg);
    border: 1px solid #bbf7d0;
    color: #14532d;
}

.form-feedback.error {
    display: block;
    background-color: var(--color-danger-bg);
    border: 1px solid #fecaca;
    color: #7f1d1d;
}

/* ================= PRINT STYLES ================= */
@media print {
    .site-header, .site-footer, .support-widget-float, .btn-secondary, .copy-report-btn, .button-row, .tab-group {
        display: none !important;
    }
    body, .main-wrapper, .calc-panel, .results-card {
        background: #ffffff !important;
        color: #000000 !important;
        border: none !important;
        box-shadow: none !important;
    }
    .metric-hero, .metric-cell {
        border: 1px solid #000000 !important;
    }
}