/* =========================================================================
   Balancing Equations Calculator — SEOWebChecker.com — Stylesheet
   ========================================================================= */

:root {
  --font-display: 'Outfit', sans-serif;
  --font-body: 'Inter', sans-serif;

  /* Dark theme (default) — dark navy system */
  --bg: #0a1120;
  --bg-elev-1: #111a2e;
  --bg-elev-2: #16213b;
  --bg-elev-3: #1c2947;
  --border: #263457;
  --border-soft: #1c2947;
  --text-primary: #eef2fb;
  --text-secondary: #a7b3cf;
  --text-muted: #6d7ba0;
  --accent: #5eead4;
  --accent-2: #7c9eff;
  --accent-warm: #ffb454;
  --danger: #ff6b6b;
  --success: #5eead4;
  --shadow: 0 20px 60px -20px rgba(0,0,0,0.6);
  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 22px;
}

[data-theme="light"] {
  --bg: #f5f7fc;
  --bg-elev-1: #ffffff;
  --bg-elev-2: #eef1f9;
  --bg-elev-3: #e4e9f6;
  --border: #d7deef;
  --border-soft: #e4e9f6;
  --text-primary: #101a30;
  --text-secondary: #465072;
  --text-muted: #7482a3;
  --accent: #0f9c8a;
  --accent-2: #3e63d1;
  --accent-warm: #c9791c;
  --danger: #d43f3f;
  --success: #0f9c8a;
  --shadow: 0 20px 60px -25px rgba(20,30,60,0.25);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  * { animation-duration: 0.01ms !important; animation-iteration-count: 1 !important; transition-duration: 0.01ms !important; }
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text-primary);
  font-family: var(--font-body);
  line-height: 1.6;
  overflow-x: hidden;
  transition: background .25s ease, color .25s ease;
}
body.no-scroll { overflow: hidden; }

img { max-width: 100%; display: block; }
a { color: inherit; text-decoration: none; }
h1, h2, h3, h4 { font-family: var(--font-display); margin: 0 0 .5em; line-height: 1.15; letter-spacing: -0.01em; }
p { margin: 0 0 1em; color: var(--text-secondary); }
ul { padding: 0; margin: 0; list-style: none; }
button { font-family: inherit; cursor: pointer; }
:focus-visible { outline: 2px solid var(--accent-2); outline-offset: 2px; }

.container { width: 100%; max-width: 1180px; margin: 0 auto; padding: 0 20px; }
.visually-hidden {
  position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px;
  overflow: hidden; clip: rect(0,0,0,0); white-space: nowrap; border: 0;
}
sub { font-size: .7em; }
sup { font-size: .65em; }

/* ---------------- Skip link ---------------- */
.skip-link {
  position: absolute; left: -999px; top: 0; background: var(--accent-2); color: #05122b;
  padding: 10px 16px; z-index: 999; border-radius: 0 0 8px 0;
}
.skip-link:focus { left: 0; }

/* ---------------- Header ---------------- */
.site-header {
  position: sticky; top: 0; z-index: 100;
  background: color-mix(in srgb, var(--bg-elev-1) 92%, transparent);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--border-soft);
}
.header-inner { display: flex; align-items: center; justify-content: space-between; height: 68px; gap: 16px; }
.brand { display: flex; align-items: center; gap: 10px; font-family: var(--font-display); font-weight: 700; font-size: 1.05rem; }
.brand-mark {
  width: 34px; height: 34px; border-radius: 10px;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  display: flex; align-items: center; justify-content: center; color: #05122b; font-weight: 800; font-size: .95rem;
  flex-shrink: 0;
}

.primary-nav { display: none; }
@media (min-width: 960px) {
  .primary-nav { display: flex; align-items: center; gap: 4px; }
}
.primary-nav > ul { display: flex; align-items: center; gap: 2px; position: relative; }
.primary-nav a, .primary-nav > ul > li.has-dropdown > button {
  display: flex; align-items: center; gap: 6px;
  padding: 10px 14px; border-radius: var(--radius-sm); font-size: .92rem; font-weight: 500;
  color: var(--text-secondary); background: none; border: none; white-space: nowrap;
}
.primary-nav a:hover, .primary-nav > ul > li.has-dropdown > button:hover { color: var(--text-primary); background: var(--bg-elev-2); }

.has-dropdown { position: relative; }
.has-dropdown .chev { transition: transform .18s ease; font-size: .7em; }
.has-dropdown.open .chev { transform: rotate(180deg); }
.dropdown-panel {
  position: absolute;
  top: 100%;
  left: 0;
  min-width: 300px;
  background: var(--bg-elev-1);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow);
  padding: 10px;
  opacity: 0;
  visibility: hidden;
  transform: translateY(6px);
  transition: opacity .16s ease, transform .16s ease, visibility .16s ease;
  z-index: 50;
}
.has-dropdown.open .dropdown-panel { opacity: 1; visibility: visible; transform: translateY(0); }
.dropdown-panel a { display: block; padding: 9px 12px; border-radius: var(--radius-sm); font-size: .88rem; color: var(--text-secondary); }
.dropdown-panel a:hover { background: var(--bg-elev-2); color: var(--accent); }

.header-actions { display: flex; align-items: center; gap: 10px; }
.theme-toggle {
  width: 40px; height: 40px; border-radius: 50%; border: 1px solid var(--border);
  background: var(--bg-elev-2); color: var(--text-primary); display: flex; align-items: center; justify-content: center;
  font-size: 1rem; flex-shrink: 0;
}
.theme-toggle .icon-moon { display: inline; }
.theme-toggle .icon-sun { display: none; }
[data-theme="light"] .theme-toggle .icon-moon { display: none; }
[data-theme="light"] .theme-toggle .icon-sun { display: inline; }

.nav-toggle {
  display: flex; flex-direction: column; justify-content: center; gap: 5px;
  width: 40px; height: 40px; border-radius: var(--radius-sm); border: 1px solid var(--border);
  background: var(--bg-elev-2);
}
@media (min-width: 960px) { .nav-toggle { display: none; } }
.nav-toggle span { width: 18px; height: 2px; background: var(--text-primary); margin: 0 auto; border-radius: 2px; }

.nav-drawer {
  display: none;
  position: fixed; inset: 68px 0 0 0; z-index: 90;
  background: var(--bg); overflow-y: auto;
  padding: 20px;
}
.nav-drawer.open { display: block; }
@media (min-width: 960px) { .nav-drawer { display: none !important; } }
.nav-drawer ul { display: flex; flex-direction: column; gap: 2px; }
.nav-drawer a, .nav-drawer summary { padding: 14px 10px; border-bottom: 1px solid var(--border-soft); font-size: 1rem; display: block; }
.nav-drawer details ul { padding-left: 12px; }
.nav-drawer details ul a { padding: 10px; font-size: .9rem; color: var(--text-secondary); border-bottom: none; }

/* ---------------- Breadcrumb ---------------- */
.breadcrumb-bar { border-bottom: 1px solid var(--border-soft); background: var(--bg-elev-1); }
.breadcrumb-list { display: flex; flex-wrap: wrap; align-items: center; gap: 6px; padding: 12px 0; font-size: .82rem; color: var(--text-muted); }
.breadcrumb-list a { color: var(--text-muted); }
.breadcrumb-list a:hover { color: var(--accent); }
.breadcrumb-list li[aria-current] { color: var(--text-secondary); }
.breadcrumb-list meta { display: none; }

/* ---------------- Hero ---------------- */
.hero { padding: 56px 0 40px; position: relative; overflow: hidden; }
.hero::before {
  content: ""; position: absolute; inset: -20% -10% auto -10%; height: 480px;
  background: radial-gradient(60% 60% at 30% 20%, color-mix(in srgb, var(--accent) 18%, transparent), transparent 70%),
              radial-gradient(50% 50% at 80% 10%, color-mix(in srgb, var(--accent-2) 16%, transparent), transparent 70%);
  pointer-events: none; z-index: 0;
}
.hero-inner { position: relative; z-index: 1; display: grid; gap: 28px; }
.eyebrow {
  display: inline-flex; align-items: center; gap: 8px; font-size: .78rem; font-weight: 600;
  letter-spacing: .06em; text-transform: uppercase; color: var(--accent);
  background: color-mix(in srgb, var(--accent) 12%, transparent); padding: 6px 12px; border-radius: 999px;
  border: 1px solid color-mix(in srgb, var(--accent) 30%, transparent);
}
.hero h1 { font-size: clamp(2rem, 5vw, 3.1rem); max-width: 18ch; }
.hero-sub { font-size: 1.05rem; max-width: 62ch; }

/* Calculator card */
.calc-card {
  background: var(--bg-elev-1); border: 1px solid var(--border); border-radius: var(--radius-lg);
  padding: 24px; box-shadow: var(--shadow);
}
.calc-card label { display: block; font-weight: 600; font-size: .9rem; margin-bottom: 8px; }
.input-row { display: flex; flex-direction: column; gap: 10px; }
.equation-input {
  width: 100%; font-size: 1.15rem; font-family: 'Inter', monospace; padding: 16px 18px;
  background: var(--bg-elev-2); border: 1.5px solid var(--border); border-radius: var(--radius-md);
  color: var(--text-primary);
}
.equation-input:focus { border-color: var(--accent-2); }
.input-meta { display: flex; justify-content: space-between; font-size: .78rem; color: var(--text-muted); }
.live-validation { min-height: 1.2em; }
.live-validation.warn { color: var(--accent-warm); }
.live-validation.ok { color: var(--success); }

.examples-row { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 14px; }
.example-chip {
  border: 1px solid var(--border); background: var(--bg-elev-2); color: var(--text-secondary);
  padding: 7px 12px; border-radius: 999px; font-size: .82rem; font-family: 'Inter', monospace;
}
.example-chip:hover { border-color: var(--accent-2); color: var(--text-primary); }

.calc-actions { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 18px; }
.btn {
  display: inline-flex; align-items: center; justify-content: center; gap: 8px;
  padding: 13px 22px; border-radius: var(--radius-sm); font-weight: 600; font-size: .95rem;
  border: 1px solid transparent; transition: transform .1s ease, opacity .15s ease;
}
.btn:active { transform: translateY(1px); }
.btn-primary { background: linear-gradient(135deg, var(--accent), var(--accent-2)); color: #05122b; }
.btn-primary:disabled { opacity: .6; cursor: progress; }
.btn-secondary { background: var(--bg-elev-2); border-color: var(--border); color: var(--text-primary); }
.btn-secondary:hover { border-color: var(--accent-2); }
.btn-ghost { background: transparent; border-color: var(--border); color: var(--text-secondary); }

.error-box {
  margin-top: 16px; padding: 14px 16px; border-radius: var(--radius-md);
  background: color-mix(in srgb, var(--danger) 14%, transparent); border: 1px solid color-mix(in srgb, var(--danger) 45%, transparent);
  color: var(--danger); font-size: .9rem;
}

/* Share row */
.share-row { display: flex; flex-wrap: wrap; align-items: center; gap: 10px; margin: 28px 0 6px; }
.share-row span { font-size: .85rem; color: var(--text-muted); font-weight: 600; }
.share-btn {
  width: 38px; height: 38px; border-radius: 50%; display: flex; align-items: center; justify-content: center;
  background: var(--bg-elev-2); border: 1px solid var(--border); font-size: .95rem; color: var(--text-secondary);
}
.share-btn:hover { color: var(--accent); border-color: var(--accent); }

/* ---------------- Tool strips (Chemistry / Maths quick links) ---------------- */
.tool-strip { padding: 36px 0 8px; }
.tool-strip h2 { font-size: 1.2rem; }
.tool-strip-scroller {
  display: flex; gap: 10px; overflow-x: auto; padding-bottom: 6px; scrollbar-width: thin;
  -webkit-overflow-scrolling: touch;
}
.tool-strip-scroller::-webkit-scrollbar { height: 6px; }
.tool-strip-scroller::-webkit-scrollbar-thumb { background: var(--border); border-radius: 4px; }
.tool-pill {
  flex: 0 0 auto; padding: 10px 16px; background: var(--bg-elev-1); border: 1px solid var(--border);
  border-radius: 999px; font-size: .85rem; color: var(--text-secondary); white-space: nowrap;
}
.tool-pill:hover { color: var(--accent); border-color: var(--accent); }

/* ---------------- Results ---------------- */
.results-section { padding: 40px 0; scroll-margin-top: 90px; }
.result-card {
  background: var(--bg-elev-1); border: 1px solid var(--border); border-radius: var(--radius-lg);
  padding: 28px; box-shadow: var(--shadow);
}
.result-equation {
  font-family: var(--font-display); font-size: clamp(1.2rem, 3.4vw, 1.9rem); font-weight: 600;
  display: flex; flex-wrap: wrap; align-items: baseline; gap: 8px; padding: 18px 0;
  border-top: 1px solid var(--border-soft); border-bottom: 1px solid var(--border-soft); margin: 16px 0 22px;
}
.result-equation .coef { color: var(--accent); font-weight: 800; }
.result-equation .formula { color: var(--text-primary); }
.result-equation .plus { color: var(--text-muted); margin: 0 4px; }
.result-equation .arrow { color: var(--accent-2); margin: 0 10px; font-size: 1.1em; }

.result-columns { display: grid; gap: 24px; }
@media (min-width: 780px) { .result-columns { grid-template-columns: 1fr 1fr; } }
.steps-list { display: flex; flex-direction: column; gap: 10px; counter-reset: step; }
.steps-list li { position: relative; padding-left: 34px; font-size: .92rem; color: var(--text-secondary); }
.steps-list li::before {
  counter-increment: step; content: counter(step); position: absolute; left: 0; top: -1px;
  width: 24px; height: 24px; border-radius: 50%; background: var(--bg-elev-3); color: var(--accent);
  font-size: .75rem; font-weight: 700; display: flex; align-items: center; justify-content: center;
}
.coeff-table { width: 100%; border-collapse: collapse; font-size: .88rem; }
.coeff-table th, .coeff-table td { text-align: left; padding: 9px 10px; border-bottom: 1px solid var(--border-soft); }
.coeff-table th { color: var(--text-muted); font-weight: 600; font-size: .78rem; text-transform: uppercase; letter-spacing: .04em; }
.coeff-table td.ok { color: var(--success); font-weight: 600; }
.coeff-table td.bad { color: var(--danger); font-weight: 600; }

.output-actions { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 24px; }

/* ---------------- Features ---------------- */
.section { padding: 64px 0; }
.section-head { max-width: 640px; margin-bottom: 36px; }
.section-head .eyebrow { margin-bottom: 12px; }
.feature-grid { display: grid; gap: 18px; grid-template-columns: repeat(auto-fit, minmax(240px, 1fr)); }
.feature-card {
  background: var(--bg-elev-1); border: 1px solid var(--border); border-radius: var(--radius-md);
  padding: 22px; transition: border-color .15s ease, transform .15s ease;
}
.feature-card:hover { border-color: var(--accent-2); transform: translateY(-2px); }
.feature-icon {
  width: 40px; height: 40px; border-radius: 10px; background: color-mix(in srgb, var(--accent-2) 16%, transparent);
  display: flex; align-items: center; justify-content: center; font-size: 1.2rem; margin-bottom: 14px;
}
.feature-card h3 { font-size: 1.02rem; }
.feature-card p { font-size: .9rem; margin: 0; }

/* ---------------- How it works ---------------- */
.steps-grid { display: grid; gap: 20px; grid-template-columns: repeat(auto-fit, minmax(220px, 1fr)); }
.step-block { position: relative; padding-top: 8px; }
.step-num { font-family: var(--font-display); font-size: 2.2rem; font-weight: 800; color: color-mix(in srgb, var(--accent-2) 60%, var(--border)); }
.step-block h3 { font-size: 1rem; margin-top: 4px; }
.step-block p { font-size: .9rem; }

/* ---------------- Content / article ---------------- */
.article-content h2 { font-size: 1.4rem; margin-top: 1.6em; }
.article-content h3 { font-size: 1.1rem; margin-top: 1.2em; }
.article-content p { font-size: .96rem; max-width: 74ch; }
.article-content ul { list-style: disc; padding-left: 1.4em; margin-bottom: 1.2em; }
.article-content li { font-size: .95rem; color: var(--text-secondary); margin-bottom: .4em; }
.example-table-wrap { overflow-x: auto; margin: 20px 0; }
.example-table { width: 100%; border-collapse: collapse; min-width: 520px; font-size: .88rem; }
.example-table th, .example-table td { border: 1px solid var(--border-soft); padding: 10px 12px; text-align: left; }
.example-table th { background: var(--bg-elev-2); }

/* ---------------- FAQ ---------------- */
.faq-list { display: flex; flex-direction: column; gap: 10px; max-width: 800px; }
.faq-item { border: 1px solid var(--border); border-radius: var(--radius-md); background: var(--bg-elev-1); overflow: hidden; }
.faq-item button {
  width: 100%; display: flex; justify-content: space-between; align-items: center; gap: 12px;
  background: none; border: none; padding: 18px 20px; font-size: .98rem; font-weight: 600; color: var(--text-primary);
  text-align: left;
}
.faq-item .faq-plus { transition: transform .18s ease; color: var(--accent); font-size: 1.2rem; }
.faq-item.open .faq-plus { transform: rotate(45deg); }
.faq-answer { max-height: 0; overflow: hidden; transition: max-height .22s ease; }
.faq-item.open .faq-answer { max-height: 300px; }
.faq-answer p { padding: 0 20px 18px; font-size: .92rem; }

/* ---------------- CTA ---------------- */
.cta-section {
  background: linear-gradient(135deg, var(--bg-elev-2), var(--bg-elev-1));
  border-top: 1px solid var(--border-soft); border-bottom: 1px solid var(--border-soft);
}
.cta-inner { text-align: center; max-width: 640px; margin: 0 auto; }
.cta-buttons { display: flex; flex-wrap: wrap; justify-content: center; gap: 12px; margin-top: 22px; }

/* ---------------- Footer ---------------- */
.site-footer { background: var(--bg-elev-1); border-top: 1px solid var(--border-soft); padding: 50px 0 22px; }
.footer-grid { display: grid; gap: 28px; grid-template-columns: repeat(2, 1fr); margin-bottom: 32px; }
@media (min-width: 720px) { .footer-grid { grid-template-columns: repeat(4, 1fr); } }
.footer-col h4 { font-size: .82rem; text-transform: uppercase; letter-spacing: .05em; color: var(--text-muted); margin-bottom: 14px; }
.footer-col ul { display: flex; flex-direction: column; gap: 9px; }
.footer-col a { font-size: .86rem; color: var(--text-secondary); }
.footer-col a:hover { color: var(--accent); }
.footer-bottom {
  border-top: 1px solid var(--border-soft); padding-top: 20px; display: flex; flex-wrap: wrap;
  justify-content: space-between; gap: 12px; font-size: .82rem; color: var(--text-muted);
}
.footer-bottom-links { display: flex; flex-wrap: wrap; gap: 16px; }
.footer-bottom-links a { color: var(--text-muted); }
.footer-bottom-links a:hover { color: var(--accent); }
.footer-disclaimer { font-size: .78rem; color: var(--text-muted); max-width: 900px; margin: 0 0 20px; }

/* ---------------- Cookie banner ---------------- */
.cookie-banner {
  position: fixed; left: 16px; right: 16px; bottom: 16px; z-index: 200;
  background: var(--bg-elev-1); border: 1px solid var(--border); border-radius: var(--radius-md);
  box-shadow: var(--shadow); padding: 18px; display: flex; flex-wrap: wrap; align-items: center; gap: 14px;
  max-width: 720px; margin: 0 auto;
}
.cookie-banner[hidden] { display: none; }
.cookie-banner p { margin: 0; font-size: .86rem; flex: 1 1 260px; }
.cookie-banner a { color: var(--accent); }

/* ---------------- Utility ---------------- */
.grid-2 { display: grid; gap: 20px; }
@media (min-width: 760px) { .grid-2 { grid-template-columns: 1fr 1fr; } }