/* ── TOKENS ─────────────────────────────────── */
:root {
  --bg:         #f0f2f5;
  --surface:    #ffffff;
  --surface2:   #f5f7fa;
  --border:     #e2e6ed;
  --text:       #1a1d23;
  --muted:      #8892a4;
  --accent:     #2563eb;
  --accent-lt:  #dbeafe;
  --op:         #1e40af;
  --op-lt:      #eff6ff;
  --eq:         #2563eb;
  --fn:         #6d28d9;
  --fn-lt:      #ede9fe;
  --clear:      #dc2626;
  --clear-lt:   #fee2e2;
  --num-hover:  #f0f4ff;
  --shadow:     0 2px 16px rgba(0,0,0,0.08), 0 1px 3px rgba(0,0,0,0.06);
  --shadow-btn: 0 1px 3px rgba(0,0,0,0.1);

  --font-main: 'Outfit', sans-serif;
  --font-mono: 'JetBrains Mono', monospace;
  --radius: 14px;
  --radius-sm: 9px;
  --radius-btn: 11px;
}

[data-theme="night"] {
  --bg:         #0d0f14;
  --surface:    #161921;
  --surface2:   #1e2130;
  --border:     #272b38;
  --text:       #e8ecf4;
  --muted:      #555f75;
  --accent:     #3b82f6;
  --accent-lt:  #1e3a5f;
  --op:         #60a5fa;
  --op-lt:      #1a2d4a;
  --eq:         #3b82f6;
  --fn:         #a78bfa;
  --fn-lt:      #2d1f5e;
  --clear:      #f87171;
  --clear-lt:   #3b1414;
  --num-hover:  #1e2436;
  --shadow:     0 2px 20px rgba(0,0,0,0.4);
  --shadow-btn: 0 1px 4px rgba(0,0,0,0.3);
}

*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }

body {
  font-family: var(--font-main);
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  transition: background 0.3s, color 0.3s;
}

/* ── HEADER ─────────────────────────────────── */
.header {
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 50;
  transition: background 0.3s, border-color 0.3s;
}

.header-inner {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 24px;
  height: 56px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}

.logo { text-decoration: none; font-weight: 700; font-size: 1rem; color: var(--text); }
.logo span { color: var(--accent); }

.nav { display: flex; gap: 20px; }
.nav a { color: var(--muted); text-decoration: none; font-size: 0.875rem; transition: color 0.2s; }
.nav a:hover { color: var(--accent); }

.theme-toggle {
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 5px 14px;
  font-size: 0.8rem;
  font-family: var(--font-main);
  color: var(--text);
  cursor: pointer;
  transition: all 0.2s;
}
.theme-toggle:hover { border-color: var(--accent); color: var(--accent); }

/* ── PAGE LAYOUT ────────────────────────────── */
.section { padding: 40px 24px 80px; }
.container { max-width: 1200px; margin: 0 auto; }

.page-layout {
  display: grid;
  grid-template-columns: 1fr 220px;
  gap: 32px;
  align-items: start;
}
@media (max-width: 800px) { .page-layout { grid-template-columns: 1fr; } }

.section-title {
  font-size: 1.6rem;
  font-weight: 700;
  margin-bottom: 6px;
  letter-spacing: -0.5px;
}

.section-desc { color: var(--muted); font-size: 0.9rem; margin-bottom: 24px; }

/* ── CALCULATOR SHELL ───────────────────────── */
.calculator {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  max-width: 480px;
  overflow: hidden;
  transition: background 0.3s, border-color 0.3s;
}

/* ── MODE TABS ───────────────────────────────── */
.mode-tabs {
  display: flex;
  background: var(--surface2);
  border-bottom: 1px solid var(--border);
}

.mode-tab {
  flex: 1;
  padding: 11px;
  border: none;
  background: none;
  font-family: var(--font-main);
  font-size: 0.82rem;
  font-weight: 500;
  color: var(--muted);
  cursor: pointer;
  transition: all 0.2s;
  border-bottom: 2px solid transparent;
  margin-bottom: -1px;
}

.mode-tab.active {
  color: var(--accent);
  border-bottom-color: var(--accent);
  background: var(--surface);
}

/* ── DISPLAY ─────────────────────────────────── */
.display-wrap {
  padding: 16px 20px 12px;
  background: var(--surface);
  border-bottom: 1px solid var(--border);
}

.display-expr {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  color: var(--muted);
  min-height: 18px;
  text-align: right;
  margin-bottom: 4px;
  letter-spacing: 0.02em;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.display-main {
  font-family: var(--font-mono);
  font-size: 2.4rem;
  font-weight: 500;
  color: var(--text);
  text-align: right;
  min-height: 52px;
  line-height: 1.2;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
  transition: color 0.2s;
  letter-spacing: -1px;
}

.display-main.error { color: var(--clear); font-size: 1.4rem; }

.display-meta {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 6px;
}

.angle-toggle {
  background: var(--accent-lt);
  border: none;
  border-radius: 999px;
  padding: 3px 10px;
  font-size: 0.7rem;
  font-family: var(--font-mono);
  color: var(--accent);
  cursor: pointer;
  font-weight: 600;
  transition: all 0.2s;
}
.angle-toggle:hover { background: var(--accent); color: #fff; }

.mem-indicator {
  font-family: var(--font-mono);
  font-size: 0.68rem;
  color: var(--muted);
  letter-spacing: 0.05em;
  min-width: 60px;
}

/* ── BUTTON GRID ─────────────────────────────── */
.btn-grid {
  display: grid;
  gap: 6px;
  padding: 14px;
}

/* Basic: 4 cols */
.btn-grid.basic { grid-template-columns: repeat(4, 1fr); }

/* Scientific: 5 cols */
.btn-grid.sci { grid-template-columns: repeat(5, 1fr); }

.calc-btn {
  height: 52px;
  border: none;
  border-radius: var(--radius-btn);
  font-family: var(--font-mono);
  font-size: 0.88rem;
  font-weight: 500;
  cursor: pointer;
  transition: all 0.12s;
  box-shadow: var(--shadow-btn);
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 2px;
  letter-spacing: -0.3px;
  position: relative;
  overflow: hidden;
}

.calc-btn::after {
  content: '';
  position: absolute;
  inset: 0;
  background: rgba(255,255,255,0);
  transition: background 0.15s;
  border-radius: inherit;
}

.calc-btn:active::after { background: rgba(255,255,255,0.15); }
.calc-btn:active { transform: scale(0.94); }

/* Number */
.calc-btn.num {
  background: var(--surface2);
  color: var(--text);
  font-size: 1rem;
  font-weight: 600;
}
.calc-btn.num:hover { background: var(--num-hover); color: var(--accent); }

/* Operator */
.calc-btn.op {
  background: var(--op-lt);
  color: var(--op);
  font-size: 1.1rem;
}
.calc-btn.op:hover { background: var(--op); color: #fff; }

/* Equals */
.calc-btn.eq {
  background: var(--accent);
  color: #fff;
  font-size: 1.2rem;
  font-weight: 700;
}
.calc-btn.eq:hover { filter: brightness(1.12); }

/* Function */
.calc-btn.fn {
  background: var(--fn-lt);
  color: var(--fn);
  font-size: 0.78rem;
}
.calc-btn.fn:hover { background: var(--fn); color: #fff; }

/* Clear */
.calc-btn.clr {
  background: var(--clear-lt);
  color: var(--clear);
  font-weight: 700;
}
.calc-btn.clr:hover { background: var(--clear); color: #fff; }

/* Special util */
.calc-btn.util {
  background: var(--surface2);
  color: var(--muted);
}
.calc-btn.util:hover { color: var(--text); background: var(--border); }

.calc-btn.span2 { grid-column: span 2; }
.calc-btn.span3 { grid-column: span 3; }

/* ── HISTORY ─────────────────────────────────── */
.history-wrap {
  border-top: 1px solid var(--border);
  padding: 0 14px 14px;
}

.history-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 10px 0 6px;
}

.history-label {
  font-size: 0.72rem;
  font-family: var(--font-mono);
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.06em;
}

.btn-clear-hist {
  background: none;
  border: none;
  font-size: 0.72rem;
  font-family: var(--font-main);
  color: var(--muted);
  cursor: pointer;
  padding: 2px 6px;
  border-radius: 4px;
  transition: color 0.2s;
}
.btn-clear-hist:hover { color: var(--clear); }

.history-list {
  max-height: 110px;
  overflow-y: auto;
  display: flex;
  flex-direction: column;
  gap: 3px;
}

.history-list::-webkit-scrollbar { width: 4px; }
.history-list::-webkit-scrollbar-thumb { background: var(--border); border-radius: 4px; }

.history-item {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 5px 8px;
  border-radius: 6px;
  cursor: pointer;
  transition: background 0.15s;
}
.history-item:hover { background: var(--surface2); }

.history-expr {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--muted);
  flex: 1;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.history-result {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: var(--accent);
  font-weight: 600;
  margin-left: 10px;
  flex-shrink: 0;
}

.history-empty {
  font-size: 0.78rem;
  color: var(--muted);
  text-align: center;
  padding: 12px 0;
  font-family: var(--font-mono);
}

/* ── SEO CONTENT ─────────────────────────────── */
.seo-content {
  margin-top: 36px;
  max-width: 600px;
}
.seo-content h2 { font-size: 1.2rem; font-weight: 700; margin-bottom: 10px; }
.seo-content h3 { font-size: 1rem; font-weight: 600; margin: 20px 0 8px; color: var(--text); }
.seo-content p, .seo-content li { font-size: 0.875rem; color: var(--muted); line-height: 1.75; }
.seo-content ul { padding-left: 18px; }
.seo-content li { margin-bottom: 4px; }

.faq-block { margin-top: 8px; }
.faq-q {
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text);
  cursor: pointer;
  padding: 12px 0;
  border-bottom: 1px solid var(--border);
  display: flex;
  justify-content: space-between;
}
.faq-q::after { content: '+'; color: var(--accent); }
.faq-item.open .faq-q::after { content: '−'; }
.faq-a { font-size: 0.875rem; color: var(--muted); padding: 10px 0 4px; display: none; line-height: 1.7; }
.faq-item.open .faq-a { display: block; }

/* ── SIDEBAR ─────────────────────────────────── */
.right-column h2 { font-size: 1rem; font-weight: 700; margin-bottom: 12px; }

.quick-links { display: flex; flex-direction: column; gap: 8px; }
.quick-links a {
  display: block;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 10px 14px;
  font-size: 0.85rem;
  color: var(--text);
  text-decoration: none;
  transition: all 0.2s;
}
.quick-links a:hover { border-color: var(--accent); color: var(--accent); }

/* ── FOOTER ──────────────────────────────────── */
.footer {
  background: var(--surface);
  border-top: 1px solid var(--border);
  text-align: center;
  padding: 20px;
  font-size: 0.8rem;
  color: var(--muted);
}

/* ── RIPPLE ──────────────────────────────────── */
.ripple {
  position: absolute;
  border-radius: 50%;
  background: rgba(255,255,255,0.3);
  transform: scale(0);
  animation: ripple 0.4s linear;
  pointer-events: none;
}
@keyframes ripple { to { transform: scale(4); opacity: 0; } }