:root {
  --bg: #121318;
  --bg-accent: #181a21;
  --surface: #1d1e25;
  --surface-2: #262832;
  --surface-3: #2f313d;
  --text: #f2f1ed;
  --text-dim: #93949e;
  --line: color-mix(in srgb, var(--surface-3) 70%, transparent);
  --accent-op: #ff9f4a;
  --accent-op-text: #1a1206;
  --accent-eq: #6ee7c9;
  --accent-eq-text: #0a1f1a;
  --danger: #ff6b6b;
  --radius-lg: 22px;
  --radius-md: 14px;
  --shadow-card: 0 24px 50px -28px rgba(0, 0, 0, 0.65);
  --font-display: "Space Grotesk", sans-serif;
  --font-ui: "Inter", sans-serif;
  --header-h: 64px;
  color-scheme: dark;
}

:root[data-theme="light"] {
  --bg: #f4f3ef;
  --bg-accent: #eceae4;
  --surface: #ffffff;
  --surface-2: #f3f1eb;
  --surface-3: #e4e2db;
  --text: #1b1c20;
  --text-dim: #6c6d76;
  --accent-op: #e9772f;
  --accent-op-text: #fff8f1;
  --accent-eq: #128a6e;
  --accent-eq-text: #f0fffa;
  --shadow-card: 0 20px 40px -28px rgba(30, 25, 15, 0.28);
  color-scheme: light;
}

* { box-sizing: border-box; }

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background:
    radial-gradient(1200px 500px at 10% -10%, color-mix(in srgb, var(--accent-eq) 8%, transparent), transparent 50%),
    var(--bg);
  color: var(--text);
  font-family: var(--font-ui);
  min-height: 100vh;
  line-height: 1.5;
  transition: background 0.35s ease, color 0.35s ease;
}

a {
  color: inherit;
  text-decoration: none;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 20;
  height: var(--header-h);
  display: flex;
  align-items: center;
  gap: 20px;
  padding: 0 22px;
  background: color-mix(in srgb, var(--bg) 86%, transparent);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--line);
}

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-right: auto;
}
.brand-mark {
  width: 34px;
  height: 34px;
  border-radius: 9px;
  display: grid;
  place-items: center;
  background: var(--accent-eq);
  color: var(--accent-eq-text);
  font-family: var(--font-display);
  font-weight: 700;
  font-size: 1.15rem;
}
.brand strong {
  display: block;
  font-family: var(--font-display);
  font-size: 1.05rem;
  line-height: 1.1;
}
.brand small {
  color: var(--text-dim);
  font-size: 0.72rem;
}

.nav {
  display: flex;
  gap: 18px;
  font-size: 0.88rem;
  color: var(--text-dim);
}
.nav a:hover {
  color: var(--text);
}

.theme-toggle {
  width: 40px;
  height: 40px;
  border-radius: 50%;
  border: 1px solid var(--surface-3);
  background: var(--surface);
  color: var(--text);
  display: grid;
  place-items: center;
  cursor: pointer;
}
.theme-toggle svg { width: 18px; height: 18px; }
.theme-toggle .icon-moon { display: none; }
:root[data-theme="light"] .theme-toggle .icon-sun { display: none; }
:root[data-theme="light"] .theme-toggle .icon-moon { display: block; }

.hero {
  max-width: 1180px;
  margin: 0 auto;
  padding: 36px 22px 8px;
}
.eyebrow {
  margin: 0 0 8px;
  color: var(--accent-eq);
  font-size: 0.78rem;
  font-weight: 600;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}
.hero h1 {
  font-family: var(--font-display);
  font-size: clamp(1.7rem, 4vw, 2.35rem);
  line-height: 1.15;
  margin: 0 0 10px;
  font-weight: 600;
}
.lede {
  margin: 0;
  max-width: 62ch;
  color: var(--text-dim);
  font-size: 1rem;
}

.workspace {
  max-width: 1180px;
  margin: 0 auto;
  padding: 28px 22px 40px;
  display: grid;
  grid-template-columns: minmax(0, 400px) minmax(0, 1fr);
  gap: 22px;
  align-items: start;
}

.calc {
  background: var(--surface);
  border-radius: var(--radius-lg);
  padding: 18px;
  box-shadow: var(--shadow-card);
  border: 1px solid var(--line);
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.calc-toolbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
}

.mode-switch {
  display: flex;
  background: var(--surface-2);
  border-radius: 999px;
  padding: 3px;
}
.mode-btn {
  border: none;
  background: transparent;
  color: var(--text-dim);
  font-family: var(--font-ui);
  font-size: 0.78rem;
  font-weight: 600;
  padding: 6px 12px;
  border-radius: 999px;
  cursor: pointer;
}
.mode-btn.is-active {
  background: var(--surface);
  color: var(--text);
  box-shadow: 0 1px 4px rgba(0,0,0,.12);
}

.toolbar-actions {
  display: flex;
  align-items: center;
  gap: 8px;
}
.mem-badge {
  font-size: 0.72rem;
  font-weight: 700;
  color: var(--accent-eq);
  border: 1px solid color-mix(in srgb, var(--accent-eq) 40%, transparent);
  border-radius: 6px;
  padding: 2px 7px;
}
.text-btn {
  border: none;
  background: none;
  color: var(--text-dim);
  font-size: 0.78rem;
  cursor: pointer;
  padding: 4px 2px;
}
.text-btn:hover { color: var(--text); }

.display {
  background: var(--surface-2);
  border-radius: var(--radius-md);
  padding: 18px 16px 14px;
  min-height: 96px;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  gap: 4px;
}
.display-expression {
  font-size: 0.86rem;
  color: var(--text-dim);
  min-height: 1.1em;
  text-align: right;
  white-space: nowrap;
  overflow-x: auto;
}
.display-result {
  font-family: var(--font-display);
  font-weight: 600;
  font-size: clamp(2rem, 7vw, 2.55rem);
  line-height: 1.1;
  text-align: right;
  word-break: break-all;
}
.display-result.error {
  color: var(--danger);
  font-size: 1.4rem;
}

.mem-row,
.sci-row,
.keys {
  display: grid;
  gap: 8px;
}
.mem-row { grid-template-columns: repeat(5, 1fr); }
.sci-row,
.keys { grid-template-columns: repeat(4, 1fr); }
.sci-row {
  max-height: 0;
  opacity: 0;
  overflow: hidden;
  transform: translateY(-6px);
  pointer-events: none;
  transition: max-height 0.35s ease, opacity 0.28s ease, transform 0.28s ease;
}
.sci-row.is-open {
  max-height: 72px;
  opacity: 1;
  transform: none;
  pointer-events: auto;
}

.key {
  appearance: none;
  border: none;
  border-radius: 12px;
  background: var(--surface-2);
  color: var(--text);
  font-family: var(--font-display);
  font-size: 1.12rem;
  font-weight: 500;
  padding: 14px 0;
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
}
.key:hover { filter: brightness(1.1); }
.key:active,
.key.pressed { transform: scale(0.96); }
.key:focus-visible {
  outline: 2px solid var(--accent-eq);
  outline-offset: 2px;
}
.key-fn,
.key-mem {
  background: var(--surface-3);
  font-family: var(--font-ui);
  font-weight: 600;
  font-size: 0.82rem;
}
.key-mem { padding: 10px 0; }
.key-op {
  background: transparent;
  color: var(--accent-op);
  border: 1px solid color-mix(in srgb, var(--accent-op) 45%, transparent);
}
.key-op.pressed,
.key-op.active-op {
  background: var(--accent-op);
  color: var(--accent-op-text);
}
.key-eq {
  background: var(--accent-eq);
  color: var(--accent-eq-text);
  font-weight: 600;
}

.hint {
  font-size: 0.74rem;
  color: var(--text-dim);
  margin: 2px 2px 0;
}

.side {
  display: flex;
  flex-direction: column;
  gap: 14px;
}
.side-card {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius-lg);
  padding: 18px 16px;
}
.side-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
}
.side h2 {
  font-family: var(--font-display);
  font-size: 1rem;
  margin: 0 0 6px;
}
.side-note,
.history-empty {
  color: var(--text-dim);
  font-size: 0.78rem;
  margin: 0 0 10px;
}
.history {
  max-height: 280px;
  overflow-y: auto;
  display: flex;
  flex-direction: column;
  gap: 6px;
}
.history button {
  display: block;
  width: 100%;
  text-align: right;
  border: none;
  background: var(--surface-2);
  color: var(--text);
  font-family: var(--font-ui);
  font-size: 0.82rem;
  padding: 8px 10px;
  border-radius: 8px;
  cursor: pointer;
}
.history button:hover { filter: brightness(1.08); }
.tips ul {
  margin: 8px 0 0;
  padding: 0;
  list-style: none;
  color: var(--text-dim);
  font-size: 0.84rem;
}
.tips li {
  display: flex;
  justify-content: space-between;
  padding: 6px 0;
  border-bottom: 1px dashed var(--line);
}
kbd {
  font-family: var(--font-ui);
  font-size: 0.75rem;
  background: var(--surface-2);
  border: 1px solid var(--surface-3);
  border-radius: 5px;
  padding: 1px 6px;
}

.nav {
  flex-wrap: wrap;
  justify-content: flex-end;
}

.info,
.ref-block {
  max-width: 1180px;
  margin: 0 auto;
  padding: 10px 22px 48px;
}
.ref-head p,
.section-lead {
  color: var(--text-dim);
  max-width: 72ch;
  margin: 0 0 16px;
}
.subhead {
  font-family: var(--font-display);
  font-size: 1.05rem;
  margin: 22px 0 10px;
}
.formula {
  font-family: var(--font-display);
  color: var(--text);
  margin: 0 0 8px;
}
.muted { color: var(--text-dim); margin: 0; }

.pt-legend {
  display: flex;
  flex-wrap: wrap;
  gap: 8px 12px;
  margin-bottom: 14px;
  font-size: 0.75rem;
  color: var(--text-dim);
}
.pt-legend span {
  display: inline-flex;
  align-items: center;
  gap: 6px;
}
.pt-legend i {
  width: 10px;
  height: 10px;
  border-radius: 3px;
  display: inline-block;
}

.pt-wrap {
  overflow-x: auto;
  padding-bottom: 8px;
}
.pt-grid {
  display: grid;
  grid-template-columns: repeat(18, minmax(42px, 1fr));
  gap: 3px;
  min-width: 820px;
}
.el {
  border: none;
  border-radius: 6px;
  min-height: 52px;
  padding: 3px 2px;
  cursor: pointer;
  text-align: left;
  color: var(--text);
  background: var(--surface-2);
  font-family: var(--font-ui);
  line-height: 1.15;
}
.el small { display: block; font-size: 0.58rem; color: var(--text-dim); }
.el b { display: block; font-size: 0.82rem; font-family: var(--font-display); }
.el:hover,
.el.is-on { outline: 2px solid var(--accent-eq); outline-offset: 0; }
.el-empty { min-height: 52px; }

.cat-alkali { background: #5a2a2a; }
.cat-alkaline { background: #5a3d24; }
.cat-transition { background: #2a3a5a; }
.cat-post { background: #2a4a4a; }
.cat-metalloid { background: #3a4a2a; }
.cat-nonmetal { background: #2a4a32; }
.cat-halogen { background: #3a2a4a; }
.cat-noble { background: #4a2a3a; }
.cat-lanthanide { background: #4a3a2a; }
.cat-actinide { background: #4a2a2a; }

:root[data-theme="light"] .cat-alkali { background: #f3c4c4; }
:root[data-theme="light"] .cat-alkaline { background: #f3d9b8; }
:root[data-theme="light"] .cat-transition { background: #c9d6f3; }
:root[data-theme="light"] .cat-post { background: #c7e6e6; }
:root[data-theme="light"] .cat-metalloid { background: #d8e6c4; }
:root[data-theme="light"] .cat-nonmetal { background: #c8e6d2; }
:root[data-theme="light"] .cat-halogen { background: #ddc8f0; }
:root[data-theme="light"] .cat-noble { background: #f0c8d8; }
:root[data-theme="light"] .cat-lanthanide { background: #f0ddc0; }
:root[data-theme="light"] .cat-actinide { background: #f0c8c8; }

.pt-detail {
  margin-top: 14px;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 16px;
  padding: 16px 18px;
  min-height: 88px;
}
.pt-detail h3 { margin: 0 0 6px; font-family: var(--font-display); }
.pt-meta { color: var(--text-dim); font-size: 0.86rem; margin: 0 0 8px; }
.pt-detail .text-btn { color: var(--accent-eq); }

.table-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 14px;
}
.table-card {
  background: var(--bg-accent);
  border: 1px solid var(--line);
  border-radius: 16px;
  padding: 14px 16px;
}
.table-card h3 {
  margin: 0 0 10px;
  font-size: 0.95rem;
}
.table-card table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.82rem;
}
.table-card td {
  padding: 5px 0;
  border-bottom: 1px dashed var(--line);
  vertical-align: top;
}
.table-card td:first-child {
  color: var(--text);
  font-weight: 600;
  padding-right: 10px;
  white-space: nowrap;
}
.table-card td:last-child { color: var(--text-dim); }
.info h2,
.ref-block h2 {
  font-family: var(--font-display);
  font-size: 1.35rem;
  margin: 0 0 16px;
}
.faq {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 14px;
}
.faq article {
  background: var(--bg-accent);
  border: 1px solid var(--line);
  border-radius: 16px;
  padding: 16px 16px 14px;
}
.faq h3 {
  margin: 0 0 6px;
  font-size: 0.95rem;
}
.faq p {
  margin: 0;
  color: var(--text-dim);
  font-size: 0.88rem;
}

.site-footer {
  border-top: 1px solid var(--line);
  padding: 28px 22px 36px;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 24px;
  max-width: 1180px;
  margin: 0 auto;
  color: var(--text-dim);
  font-size: 0.84rem;
}
.site-footer strong {
  color: var(--text);
  font-family: var(--font-display);
}
.copy { margin-bottom: 0; }

/* Motion */
body {
  transition: background 0.45s ease, color 0.45s ease;
}
.site-header {
  transition: background 0.35s ease, border-color 0.35s ease, box-shadow 0.35s ease;
}
.brand-mark {
  transition: transform 0.35s cubic-bezier(0.22, 1, 0.36, 1);
}
.brand:hover .brand-mark { transform: rotate(-8deg) scale(1.06); }
.nav a {
  position: relative;
  transition: color 0.2s ease;
}
.nav a::after {
  content: "";
  position: absolute;
  left: 0;
  bottom: -4px;
  width: 100%;
  height: 1px;
  background: var(--accent-eq);
  transform: scaleX(0);
  transform-origin: left;
  transition: transform 0.25s ease;
}
.nav a:hover::after { transform: scaleX(1); }
.theme-toggle {
  transition: transform 0.2s ease, background 0.3s ease, border-color 0.3s ease;
}
.theme-toggle:hover { transform: translateY(-1px); }
.theme-toggle:active { transform: scale(0.94); }
.theme-toggle svg { transition: opacity 0.25s ease, transform 0.25s ease; }

.calc, .side-card, .table-card, .faq article, .pt-detail {
  transition: transform 0.35s ease, box-shadow 0.35s ease, border-color 0.35s ease, background 0.35s ease;
}
.calc:hover, .side-card:hover {
  transform: translateY(-3px);
  box-shadow: 0 28px 56px -24px rgba(0,0,0,.5);
}
.faq article:hover, .table-card:hover {
  transform: translateY(-2px);
  border-color: color-mix(in srgb, var(--accent-eq) 28%, var(--line));
}

.mode-btn { transition: background 0.25s ease, color 0.25s ease, box-shadow 0.25s ease; }
.text-btn { transition: color 0.2s ease; }
.mem-badge {
  opacity: 0;
  transform: scale(0.7);
  pointer-events: none;
  transition: opacity 0.25s ease, transform 0.25s cubic-bezier(0.22, 1, 0.36, 1);
}
.mem-badge.show {
  opacity: 1;
  transform: scale(1);
}

.display-result.tick { animation: tick 0.28s ease; }
@keyframes tick {
  0% { transform: translateY(6px); opacity: 0.45; }
  100% { transform: none; opacity: 1; }
}

.key {
  transition: transform 0.12s ease, filter 0.18s ease, background 0.18s ease, color 0.18s ease, box-shadow 0.18s ease;
}
.key:hover { filter: brightness(1.1); transform: translateY(-1px); }
.key:active, .key.pressed { transform: scale(0.94); filter: brightness(0.96); }
.history button {
  transition: filter 0.18s ease, transform 0.18s ease;
  animation: rise 0.35s ease;
}
.history button:hover { transform: translateX(-3px); }

.el {
  transition: transform 0.18s ease, outline-color 0.18s ease, filter 0.18s ease;
  animation: fadeEl 0.5s ease both;
}
.el:hover { transform: translateY(-2px) scale(1.04); z-index: 1; }
.el.is-on { transform: scale(1.06); }
@keyframes fadeEl {
  from { opacity: 0; transform: scale(0.86); }
  to { opacity: 1; transform: none; }
}

.pt-detail-inner { animation: rise 0.32s ease; }
@keyframes rise {
  from { opacity: 0; transform: translateY(10px); }
  to { opacity: 1; transform: none; }
}

.reveal {
  opacity: 0;
  transform: translateY(18px);
  transition: opacity 0.65s cubic-bezier(0.22, 1, 0.36, 1), transform 0.65s cubic-bezier(0.22, 1, 0.36, 1);
}
.reveal.in {
  opacity: 1;
  transform: none;
}

@media (max-width: 900px) {
  .workspace,
  .faq,
  .table-grid,
  .site-footer {
    grid-template-columns: 1fr;
  }
  .nav { display: none; }
}

@media (max-width: 420px) {
  .calc { padding: 14px; }
  .key { padding: 12px 0; font-size: 1.02rem; }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation: none !important;
    transition: none !important;
    scroll-behavior: auto !important;
  }
  .reveal { opacity: 1; transform: none; }
}