* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: system-ui, -apple-system, "Segoe UI", Roboto, Arial, sans-serif;
}

:root {
  --bg: #0e1014;
  --card: #171a21;
  --display: #11141a;
  --key: #222732;
  --key-h: #2b3140;
  --fn: #2d3442;
  --fn-h: #384052;
  --op: #3a2a24;
  --op-text: #ff8a5c;
  --accent: #ff5a1f;
  --accent-h: #ff7440;
  --text: #f2f4f8;
  --muted: #8b93a3;
  --err: #ff6b6b;
  --shadow: 0 20px 60px rgba(0, 0, 0, 0.5);
}

:root[data-theme="light"] {
  --bg: #d9cdc8;
  --card: #f6f2ef;
  --display: #ffffff;
  --key: #ffffff;
  --key-h: #efe9e5;
  --fn: #e7dfda;
  --fn-h: #ddd3cd;
  --op: #fde6dc;
  --op-text: #d4400d;
  --accent: #ff5a1f;
  --accent-h: #e84c12;
  --text: #1c1917;
  --muted: #7a716b;
  --err: #c0392b;
  --shadow: 0 20px 50px rgba(80, 50, 40, 0.25);
}

body {
  min-height: 100dvh;
  display: grid;
  place-items: center;
  padding: 1rem;
  background: var(--bg);
  color: var(--text);
}

.calc {
  width: min(100%, 380px);
  padding: 16px;
  border-radius: 28px;
  background: var(--card);
  box-shadow: var(--shadow);
}

.bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 2px 4px 12px;
}

.title {
  font-weight: 600;
  color: var(--muted);
}

.tools {
  display: flex;
  gap: 4px;
}

.tool {
  width: 38px;
  height: 38px;
  display: grid;
  place-items: center;
  border: 0;
  border-radius: 12px;
  background: transparent;
  color: var(--muted);
  cursor: pointer;
}

.tool:hover,
.tool[aria-expanded="true"] {
  background: var(--key);
  color: var(--text);
}

.display {
  background: var(--display);
  border-radius: 20px;
  padding: 16px 18px;
  min-height: 118px;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  gap: 6px;
  text-align: right;
  margin-bottom: 14px;
}

.expr {
  min-height: 1.4em;
  font-size: 1.05rem;
  color: var(--muted);
  white-space: nowrap;
  overflow-x: auto;
  scrollbar-width: none;
}

.expr::-webkit-scrollbar { display: none; }

.result {
  display: block;
  font-size: 3rem;
  font-weight: 600;
  line-height: 1.1;
  white-space: nowrap;
  overflow: hidden;
  font-variant-numeric: tabular-nums;
}

.result.err {
  color: var(--err);
  font-size: 1.4rem;
}

.stage {
  position: relative;
}

.keys {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: clamp(8px, 2.4vw, 12px);
}

.key {
  aspect-ratio: 1 / 0.92;
  border: 0;
  border-radius: 18px;
  background: var(--key);
  color: var(--text);
  font-size: clamp(1.15rem, 4.6vw, 1.5rem);
  font-weight: 600;
  cursor: pointer;
  transition: background-color 0.12s, transform 0.08s;
  -webkit-tap-highlight-color: transparent;
}

.key:hover { background: var(--key-h); }
.key.fn { background: var(--fn); color: var(--text); font-size: clamp(1rem, 4vw, 1.2rem); }
.key.fn:hover { background: var(--fn-h); }
.key.op { background: var(--op); color: var(--op-text); font-size: clamp(1.4rem, 5.4vw, 1.8rem); }
.key.op:hover { filter: brightness(1.15); }
.key.eq {
  grid-column: 1 / -1;
  aspect-ratio: auto;
  height: 58px;
  background: var(--accent);
  color: #fff;
  font-size: 1.7rem;
}
.key.eq:hover { background: var(--accent-h); }
.key:active,
.key.press { transform: scale(0.94); }

:focus-visible {
  outline: 3px solid #4f8cff;
  outline-offset: 2px;
}

/* history panel covers the keypad */
.history {
  position: absolute;
  inset: 0;
  display: flex;
  flex-direction: column;
  background: var(--card);
  border-radius: 18px;
}

.history[hidden] { display: none; }

.h-head {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0 4px 8px;
  color: var(--muted);
  font-weight: 600;
}

.link {
  background: none;
  border: 0;
  color: var(--accent);
  font-weight: 600;
  cursor: pointer;
  padding: 4px 8px;
}

#h-list {
  list-style: none;
  overflow-y: auto;
  flex: 1;
  display: flex;
  flex-direction: column;
  gap: 6px;
}

#h-list li.empty {
  color: var(--muted);
  text-align: center;
  margin-top: 2rem;
}

#h-list button {
  width: 100%;
  text-align: right;
  border: 0;
  border-radius: 14px;
  background: var(--key);
  color: var(--text);
  padding: 10px 14px;
  cursor: pointer;
}

#h-list button:hover { background: var(--key-h); }
#h-list small { display: block; color: var(--muted); font-size: 0.85rem; overflow-wrap: anywhere; }
#h-list b { font-size: 1.25rem; overflow-wrap: anywhere; }

.toast {
  position: fixed;
  left: 50%;
  bottom: 1.5rem;
  transform: translate(-50%, 20px);
  background: var(--text);
  color: var(--bg);
  padding: 0.6rem 1.1rem;
  border-radius: 99px;
  font-weight: 600;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.2s, transform 0.2s;
}

.toast.show {
  opacity: 1;
  transform: translate(-50%, 0);
}

@media (max-height: 640px) {
  .key { aspect-ratio: 1 / 0.6; }
  .key.eq { height: 44px; }
  .display { min-height: 90px; padding: 10px 16px; }
  .result { font-size: 2.4rem; }
}

@media (prefers-reduced-motion: reduce) {
  .key, .toast { transition: none; }
}