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

:root {
    --clr-bg:       #f8fafc;
    --clr-surface:  #ffffff;
    --clr-primary:  #1d4ed8;
    --clr-primary-h:#1e40af;
    --clr-accent:   #f59e0b;
    --clr-text:     #1e293b;
    --clr-muted:    #64748b;
    --clr-border:   #e2e8f0;
    --clr-answer:   #065f46;
    --clr-answer-bg:#d1fae5;
    --radius:       10px;
    --shadow:       0 2px 12px rgba(0,0,0,.08);
    --shadow-lg:    0 8px 32px rgba(0,0,0,.12);
    --font:         'Segoe UI', system-ui, -apple-system, sans-serif;
}

html { scroll-behavior: smooth; }

body {
    font-family: var(--font);
    background: var(--clr-bg);
    color: var(--clr-text);
    line-height: 1.65;
    font-size: 16px;
}

a { color: var(--clr-primary); text-decoration: none; }
a:hover { text-decoration: underline; }

.container {
    max-width: 1100px;
    margin: 0 auto;
    padding: 0 1.25rem;
}

/* ── Header ─────────────────────────────────────────────────────────── */
.site-header {
    background: var(--clr-surface);
    border-bottom: 2px solid var(--clr-border);
    position: sticky;
    top: 0;
    z-index: 100;
    box-shadow: var(--shadow);
}

.site-header .container {
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 60px;
}

.site-logo {
    display: flex;
    align-items: center;
    gap: .5rem;
    font-size: 1.1rem;
    color: var(--clr-text);
    text-decoration: none;
}

.logo-icon {
    background: var(--clr-primary);
    color: #fff;
    width: 36px;
    height: 36px;
    border-radius: 8px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.2rem;
    font-weight: 900;
}

.site-nav { display: flex; gap: 1.5rem; }
.site-nav a { color: var(--clr-muted); font-size: .9rem; font-weight: 500; }
.site-nav a:hover { color: var(--clr-primary); text-decoration: none; }

/* ── Homepage ────────────────────────────────────────────────────────── */
.home-main { max-width: 1100px; margin: 0 auto; padding: 2rem 1.25rem 4rem; }

.hero {
    text-align: center;
    padding: 3rem 0 2rem;
}
.hero h1 {
    font-size: clamp(2rem, 5vw, 3rem);
    font-weight: 800;
    color: var(--clr-text);
    letter-spacing: -.02em;
}
.hero-sub {
    color: var(--clr-muted);
    font-size: 1.15rem;
    margin-top: .5rem;
}

.calculator-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 1.25rem;
    margin-top: 2rem;
}

.calc-card {
    background: var(--clr-surface);
    border: 1.5px solid var(--clr-border);
    border-radius: var(--radius);
    padding: 1.5rem;
    box-shadow: var(--shadow);
    display: flex;
    flex-direction: column;
    gap: .85rem;
    transition: box-shadow .2s;
}
.calc-card:hover { box-shadow: var(--shadow-lg); }
.calc-card h2 { font-size: 1.05rem; font-weight: 700; color: var(--clr-text); }

.calc-inputs {
    display: flex;
    align-items: center;
    gap: .5rem;
    flex-wrap: wrap;
}
.calc-inputs span { color: var(--clr-muted); font-size: .9rem; white-space: nowrap; }
.calc-inputs input {
    flex: 1;
    min-width: 70px;
    padding: .5rem .75rem;
    border: 1.5px solid var(--clr-border);
    border-radius: 6px;
    font-size: .95rem;
    color: var(--clr-text);
    background: var(--clr-bg);
    transition: border-color .15s;
}
.calc-inputs input:focus {
    outline: none;
    border-color: var(--clr-primary);
}

.calc-card button,
.widget-card button {
    background: var(--clr-primary);
    color: #fff;
    border: none;
    border-radius: 7px;
    padding: .6rem 1.25rem;
    font-size: .95rem;
    font-weight: 600;
    cursor: pointer;
    transition: background .15s, transform .1s;
    align-self: flex-start;
}
.calc-card button:hover,
.widget-card button:hover { background: var(--clr-primary-h); transform: translateY(-1px); }

.calc-result, .widget-result {
    font-size: 1.15rem;
    font-weight: 700;
    color: var(--clr-answer);
    background: var(--clr-answer-bg);
    border-radius: 7px;
    padding: .6rem 1rem;
    min-height: 2.8rem;
    display: flex;
    align-items: center;
}
.calc-result:empty, .widget-result:empty { display: none; }

.calc-example { font-size: .82rem; color: var(--clr-muted); }

/* ── Popular Calcs ───────────────────────────────────────────────────── */
.popular-calcs { margin-top: 3rem; }
.popular-calcs h2 { font-size: 1.4rem; font-weight: 700; margin-bottom: 1rem; }

.popular-grid {
    display: flex;
    flex-wrap: wrap;
    gap: .6rem;
}
.popular-link {
    background: var(--clr-surface);
    border: 1.5px solid var(--clr-border);
    border-radius: 20px;
    padding: .35rem .9rem;
    font-size: .88rem;
    color: var(--clr-primary);
    transition: background .15s, border-color .15s;
}
.popular-link:hover {
    background: var(--clr-primary);
    color: #fff;
    border-color: var(--clr-primary);
    text-decoration: none;
}

/* ── Dynamic Page Layout ─────────────────────────────────────────────── */
.page-main {
    max-width: 800px;
    margin: 0 auto;
    padding: 1.5rem 1.25rem 4rem;
}

.breadcrumb {
    font-size: .85rem;
    color: var(--clr-muted);
    margin-bottom: 1.5rem;
}
.breadcrumb a { color: var(--clr-primary); }

.answer-block { margin-bottom: 2rem; }
.answer-block h1 {
    font-size: clamp(1.5rem, 4vw, 2.2rem);
    font-weight: 800;
    letter-spacing: -.02em;
    margin-bottom: 1rem;
}

.answer-card {
    background: var(--clr-answer-bg);
    border: 2px solid #6ee7b7;
    border-radius: var(--radius);
    padding: 1.25rem 1.5rem;
}
.answer-line {
    font-size: 1.4rem;
    color: var(--clr-answer);
    font-weight: 600;
}
.answer-line strong { font-size: 1.8rem; }

/* ── Formula ─────────────────────────────────────────────────────────── */
.formula-section { margin-bottom: 2rem; }
.formula-section h2 { font-size: 1.2rem; font-weight: 700; margin-bottom: .75rem; }

.formula-box {
    background: #1e293b;
    color: #e2e8f0;
    border-radius: var(--radius);
    padding: 1.25rem 1.5rem;
    font-size: .95rem;
    font-family: 'Courier New', monospace;
    white-space: pre-wrap;
    line-height: 1.8;
}

/* ── Widget Section ──────────────────────────────────────────────────── */
.widget-section { margin-bottom: 2rem; }
.widget-section h2 { font-size: 1.2rem; font-weight: 700; margin-bottom: .75rem; }

.widget-card {
    background: var(--clr-surface);
    border: 1.5px solid var(--clr-border);
    border-radius: var(--radius);
    padding: 1.5rem;
    box-shadow: var(--shadow);
    display: flex;
    flex-direction: column;
    gap: .85rem;
}

.widget-row {
    display: flex;
    align-items: center;
    gap: .6rem;
    flex-wrap: wrap;
}
.widget-row span { color: var(--clr-muted); font-size: .9rem; }
.widget-row input {
    flex: 1;
    min-width: 80px;
    padding: .55rem .8rem;
    border: 1.5px solid var(--clr-border);
    border-radius: 7px;
    font-size: 1rem;
    color: var(--clr-text);
    background: var(--clr-bg);
    transition: border-color .15s;
}
.widget-row input:focus { outline: none; border-color: var(--clr-primary); }

/* ── FAQ ─────────────────────────────────────────────────────────────── */
.faq-section { margin-bottom: 2rem; }
.faq-section h2 { font-size: 1.2rem; font-weight: 700; margin-bottom: .75rem; }

.faq-item {
    border: 1.5px solid var(--clr-border);
    border-radius: var(--radius);
    margin-bottom: .6rem;
    overflow: hidden;
}
.faq-item summary {
    padding: 1rem 1.25rem;
    font-weight: 600;
    cursor: pointer;
    list-style: none;
    background: var(--clr-surface);
    display: flex;
    justify-content: space-between;
    align-items: center;
}
.faq-item summary::after {
    content: '+';
    font-size: 1.2rem;
    color: var(--clr-primary);
    transition: transform .2s;
}
.faq-item[open] summary::after { transform: rotate(45deg); }
.faq-item p {
    padding: .75rem 1.25rem 1rem;
    color: var(--clr-muted);
    font-size: .95rem;
    background: var(--clr-bg);
}

/* ── Related Links ───────────────────────────────────────────────────── */
.related-section { margin-bottom: 2rem; }
.related-section h2 { font-size: 1.2rem; font-weight: 700; margin-bottom: .75rem; }

.related-grid {
    display: flex;
    flex-wrap: wrap;
    gap: .6rem;
}
.related-link {
    background: var(--clr-surface);
    border: 1.5px solid var(--clr-border);
    border-radius: 20px;
    padding: .35rem .9rem;
    font-size: .88rem;
    color: var(--clr-primary);
    transition: background .15s, border-color .15s;
}
.related-link:hover {
    background: var(--clr-primary);
    color: #fff;
    border-color: var(--clr-primary);
    text-decoration: none;
}

/* ── Footer ──────────────────────────────────────────────────────────── */
.site-footer {
    background: var(--clr-surface);
    border-top: 1.5px solid var(--clr-border);
    padding: 1.5rem 0;
    margin-top: 3rem;
}
.site-footer .container {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: .6rem;
    text-align: center;
}
.footer-links { display: flex; gap: 1.25rem; }
.footer-links a { font-size: .875rem; color: var(--clr-muted); }
.footer-copy { font-size: .8rem; color: var(--clr-muted); }

/* ── Responsive ──────────────────────────────────────────────────────── */
@media (max-width: 600px) {
    .site-nav { display: none; }
    .calculator-grid { grid-template-columns: 1fr; }
    .answer-line { font-size: 1.15rem; }
    .answer-line strong { font-size: 1.4rem; }
}