/* ========================================
   RF Chain Calculator — Dark Professional Theme
   ======================================== */

/* ---------- Reset & Base ---------- */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

:root {
    --bg-primary: #0f1117;
    --bg-secondary: #1a1d27;
    --bg-card: #1e2233;
    --bg-input: #141622;
    --bg-result: #12141f;
    --border: #2a2e3f;
    --border-focus: #4a7dff;
    --text-primary: #e4e7f1;
    --text-secondary: #8b8fa3;
    --text-muted: #5c6078;
    --accent-blue: #4a7dff;
    --accent-green: #22c55e;
    --accent-orange: #f59e0b;
    --accent-red: #ef4444;
    --accent-purple: #a78bfa;
    --accent-cyan: #06b6d4;
    --shadow: 0 4px 24px rgba(0,0,0,0.3);
    --radius: 12px;
    --radius-sm: 8px;
    --transition: 0.2s ease;
}

html {
    font-size: 15px;
    scroll-behavior: smooth;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Inter', Roboto, sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
}

/* ---------- Header ---------- */
.header {
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border);
    position: sticky;
    top: 0;
    z-index: 100;
    backdrop-filter: blur(12px);
}

.header-content {
    max-width: 1400px;
    margin: 0 auto;
    padding: 1rem 1.5rem;
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

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

.logo-icon {
    font-size: 2rem;
    filter: drop-shadow(0 0 8px rgba(74,125,255,0.4));
}

.logo h1 {
    font-size: 1.4rem;
    font-weight: 700;
    background: linear-gradient(135deg, #4a7dff, #06b6d4);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    letter-spacing: -0.02em;
}

.logo .subtitle {
    font-size: 0.75rem;
    color: var(--text-muted);
    letter-spacing: 0.02em;
}

/* ---------- Navigation Tabs ---------- */
.nav-tabs {
    display: flex;
    gap: 0.25rem;
    overflow-x: auto;
    scrollbar-width: none;
    -webkit-overflow-scrolling: touch;
    padding-bottom: 2px;
}

.nav-tabs::-webkit-scrollbar {
    display: none;
}

.nav-tab {
    padding: 0.5rem 1rem;
    font-size: 0.8rem;
    font-weight: 500;
    color: var(--text-secondary);
    background: transparent;
    border: 1px solid transparent;
    border-radius: var(--radius-sm);
    cursor: pointer;
    white-space: nowrap;
    transition: all var(--transition);
    font-family: inherit;
}

.nav-tab:hover {
    color: var(--text-primary);
    background: rgba(74,125,255,0.08);
}

.nav-tab.active {
    color: var(--accent-blue);
    background: rgba(74,125,255,0.12);
    border-color: rgba(74,125,255,0.3);
}

/* ---------- Main Content ---------- */
.main-content {
    max-width: 1400px;
    margin: 0 auto;
    padding: 1.5rem;
}

/* ---------- Tab Panels ---------- */
.tab-panel {
    display: none;
    animation: fadeIn 0.3s ease;
}

.tab-panel.active {
    display: block;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(8px); }
    to { opacity: 1; transform: translateY(0); }
}

/* ---------- Panel Grid ---------- */
.panel-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
    gap: 1.25rem;
}

/* ---------- Card ---------- */
.card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 1.5rem;
    box-shadow: var(--shadow);
    transition: border-color var(--transition);
}

.card:hover {
    border-color: rgba(74,125,255,0.25);
}

.card-header {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    margin-bottom: 1.25rem;
    padding-bottom: 0.75rem;
    border-bottom: 1px solid var(--border);
}

.card-icon {
    font-size: 1.25rem;
}

.card-header h2 {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-primary);
    letter-spacing: -0.01em;
}

/* ---------- Form Elements ---------- */
.form-group {
    margin-bottom: 1rem;
}

.form-group label {
    display: block;
    font-size: 0.78rem;
    font-weight: 500;
    color: var(--text-secondary);
    margin-bottom: 0.35rem;
    letter-spacing: 0.01em;
}

input[type="number"] {
    width: 100%;
    padding: 0.6rem 0.75rem;
    font-size: 0.95rem;
    font-family: 'SF Mono', 'Fira Code', 'Cascadia Code', monospace;
    color: var(--text-primary);
    background: var(--bg-input);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    outline: none;
    transition: all var(--transition);
}

input[type="number"]:focus {
    border-color: var(--border-focus);
    box-shadow: 0 0 0 3px rgba(74,125,255,0.15);
}

input[type="number"]::-webkit-inner-spin-button,
input[type="number"]::-webkit-outer-spin-button {
    opacity: 0.5;
}

.hint {
    display: block;
    font-size: 0.72rem;
    color: var(--text-muted);
    margin-top: 0.25rem;
    font-family: 'SF Mono', 'Fira Code', monospace;
}

/* ---------- Result Box ---------- */
.result-box {
    background: var(--bg-result);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    padding: 0.75rem 1rem;
    margin-bottom: 0.75rem;
    transition: all var(--transition);
}

.result-box.highlight {
    border-color: rgba(34,197,94,0.3);
    background: rgba(34,197,94,0.04);
}

.result-box.highlight.negative {
    border-color: rgba(239,68,68,0.3);
    background: rgba(239,68,68,0.04);
}

.result-label {
    display: block;
    font-size: 0.72rem;
    font-weight: 500;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    margin-bottom: 0.2rem;
}

.result-value {
    display: block;
    font-size: 1.3rem;
    font-weight: 700;
    font-family: 'SF Mono', 'Fira Code', 'Cascadia Code', monospace;
    color: var(--accent-green);
    letter-spacing: -0.02em;
}

.result-box.highlight.negative .result-value {
    color: var(--accent-red);
}

.result-sub {
    display: block;
    font-size: 0.75rem;
    color: var(--text-secondary);
    margin-top: 0.15rem;
}

/* ---------- Formula Reference ---------- */
.formula-ref {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    margin-top: 1.25rem;
    overflow: hidden;
}

.formula-ref summary {
    padding: 0.85rem 1.25rem;
    font-size: 0.85rem;
    font-weight: 600;
    color: var(--text-secondary);
    cursor: pointer;
    background: var(--bg-secondary);
    transition: color var(--transition);
    user-select: none;
}

.formula-ref summary:hover {
    color: var(--text-primary);
}

.formula-ref[open] summary {
    border-bottom: 1px solid var(--border);
}

.formula-content {
    padding: 1rem 1.25rem;
}

.formula-item {
    padding: 0.5rem 0;
    font-size: 0.85rem;
    color: var(--text-secondary);
    border-bottom: 1px solid rgba(42,46,63,0.5);
}

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

.formula-item strong {
    color: var(--text-primary);
    font-family: 'SF Mono', 'Fira Code', monospace;
    font-size: 0.8rem;
}

.formula-item .note {
    color: var(--text-muted);
    font-size: 0.75rem;
}

/* ---------- Divider ---------- */
.divider {
    border: none;
    border-top: 1px solid var(--border);
    margin: 1.25rem 0;
}

/* ---------- Footer ---------- */
.footer {
    text-align: center;
    padding: 2rem 1.5rem;
    color: var(--text-muted);
    font-size: 0.78rem;
    border-top: 1px solid var(--border);
    margin-top: 2rem;
}

.footer-sub {
    margin-top: 0.5rem;
    color: var(--accent-orange);
    font-size: 0.72rem;
}

/* ---------- Scrollbar ---------- */
::-webkit-scrollbar {
    width: 6px;
}

::-webkit-scrollbar-track {
    background: var(--bg-primary);
}

::-webkit-scrollbar-thumb {
    background: var(--border);
    border-radius: 3px;
}

::-webkit-scrollbar-thumb:hover {
    background: var(--text-muted);
}

/* ---------- Responsive ---------- */
@media (max-width: 768px) {
    html {
        font-size: 14px;
    }

    .header-content {
        padding: 0.75rem 1rem;
    }

    .logo h1 {
        font-size: 1.2rem;
    }

    .nav-tab {
        padding: 0.4rem 0.75rem;
        font-size: 0.75rem;
    }

    .main-content {
        padding: 1rem;
    }

    .panel-grid {
        grid-template-columns: 1fr;
        gap: 1rem;
    }

    .card {
        padding: 1.25rem;
    }

    .result-value {
        font-size: 1.1rem;
    }
}

@media (max-width: 480px) {
    .header-content {
        padding: 0.5rem 0.75rem;
    }

    .nav-tab {
        padding: 0.35rem 0.6rem;
        font-size: 0.7rem;
    }

    .main-content {
        padding: 0.75rem;
    }

    .card {
        padding: 1rem;
    }
}

/* ---------- Selection ---------- */
::selection {
    background: rgba(74,125,255,0.3);
    color: #fff;
}

/* ---------- Print ---------- */
@media print {
    .header, .nav-tabs, .footer {
        display: none;
    }
    body {
        background: #fff;
        color: #000;
    }
    .card {
        break-inside: avoid;
        border: 1px solid #ddd;
    }
}