:root {
  color-scheme: light;
  --bg: #f5f7fb;
  --panel: #ffffff;
  --panel-strong: #ecf1f8;
  --text: #18212f;
  --muted: #687386;
  --line: #d9e0ea;
  --number: #f9fbfd;
  --operator: #174ea6;
  --operator-text: #ffffff;
  --accent: #0f8b6f;
  --danger: #c64747;
  --shadow: 0 22px 60px rgba(31, 45, 72, 0.16);
}

:root[data-theme="dark"] {
  color-scheme: dark;
  --bg: #111827;
  --panel: #1d2634;
  --panel-strong: #273447;
  --text: #f7fafc;
  --muted: #aab5c5;
  --line: #35445a;
  --number: #222d3d;
  --operator: #68a6ff;
  --operator-text: #08111f;
  --accent: #4fd1b0;
  --danger: #ff8a8a;
  --shadow: 0 28px 70px rgba(0, 0, 0, 0.34);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  background:
    radial-gradient(circle at 18% 12%, rgba(15, 139, 111, 0.16), transparent 28rem),
    radial-gradient(circle at 82% 8%, rgba(23, 78, 166, 0.14), transparent 24rem),
    var(--bg);
  color: var(--text);
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
}

button {
  border: 0;
  border-radius: 8px;
  color: inherit;
  cursor: pointer;
  font: inherit;
  min-width: 0;
  transition: transform 120ms ease, background 120ms ease, box-shadow 120ms ease;
}

button:active {
  transform: translateY(1px) scale(0.99);
}

button:focus-visible {
  outline: 3px solid color-mix(in srgb, var(--accent), transparent 55%);
  outline-offset: 2px;
}

.shell {
  display: grid;
  grid-template-columns: minmax(320px, 440px) minmax(260px, 360px);
  gap: 24px;
  margin: 0 auto;
  max-width: 920px;
  min-height: 100vh;
  padding: 32px 20px;
  place-content: center;
}

.calculator,
.history-panel {
  background: color-mix(in srgb, var(--panel), transparent 3%);
  border: 1px solid var(--line);
  border-radius: 8px;
  box-shadow: var(--shadow);
}

.calculator {
  padding: 18px;
}

.topbar,
.history-header {
  align-items: center;
  display: flex;
  justify-content: space-between;
  gap: 12px;
}

h1,
h2,
p {
  margin: 0;
}

h1 {
  font-size: 1.15rem;
  line-height: 1.2;
}

h2 {
  font-size: 1rem;
}

.topbar p {
  color: var(--muted);
  font-size: 0.85rem;
  margin-top: 4px;
}

.top-actions {
  display: flex;
  gap: 8px;
}

.icon-button {
  background: var(--panel-strong);
  color: var(--text);
  font-weight: 750;
  height: 40px;
  width: 48px;
}

.display {
  background: linear-gradient(180deg, var(--panel-strong), color-mix(in srgb, var(--panel-strong), var(--panel) 30%));
  border: 1px solid var(--line);
  border-radius: 8px;
  margin: 18px 0 12px;
  min-height: 132px;
  overflow: hidden;
  padding: 18px;
  text-align: right;
}

.expression {
  color: var(--muted);
  font-size: 0.95rem;
  min-height: 1.5rem;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.result {
  display: block;
  font-size: clamp(2.35rem, 9vw, 4rem);
  font-weight: 760;
  letter-spacing: 0;
  line-height: 1.08;
  margin-top: 14px;
  overflow: hidden;
  text-overflow: ellipsis;
}

.memory-strip {
  align-items: center;
  display: grid;
  grid-template-columns: repeat(4, 1fr) auto;
  gap: 8px;
  margin-bottom: 10px;
}

.memory-strip button,
.history-header button {
  background: transparent;
  border: 1px solid var(--line);
  color: var(--muted);
  font-size: 0.82rem;
  font-weight: 720;
  height: 34px;
}

.memory-strip button:hover,
.history-header button:hover {
  background: var(--panel-strong);
  color: var(--text);
}

.memory-badge {
  color: var(--accent);
  font-size: 0.78rem;
  font-weight: 760;
  padding-left: 4px;
  white-space: nowrap;
}

.keypad {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 10px;
}

.keypad button {
  aspect-ratio: 1.18;
  background: var(--number);
  border: 1px solid var(--line);
  box-shadow: 0 6px 14px rgba(20, 30, 50, 0.06);
  font-size: 1.08rem;
  font-weight: 720;
}

.keypad button:hover {
  background: var(--panel-strong);
}

.keypad .utility {
  color: var(--danger);
}

.keypad .operator,
.keypad .equals {
  background: var(--operator);
  border-color: color-mix(in srgb, var(--operator), black 10%);
  color: var(--operator-text);
}

.keypad .scientific {
  color: var(--accent);
  font-size: 0.95rem;
}

.keypad .zero {
  aspect-ratio: auto;
  grid-column: span 2;
}

.keypad .equals {
  grid-row: span 2;
}

.history-panel {
  align-self: stretch;
  display: flex;
  flex-direction: column;
  min-height: 500px;
  padding: 18px;
}

.history-list {
  display: flex;
  flex: 1;
  flex-direction: column;
  gap: 10px;
  list-style: none;
  margin: 18px 0 0;
  overflow: auto;
  padding: 0;
}

.history-list:empty::before {
  color: var(--muted);
  content: "Completed calculations appear here.";
  display: block;
  font-size: 0.92rem;
  line-height: 1.5;
  padding: 14px 2px;
}

.history-list button {
  background: var(--panel-strong);
  border: 1px solid var(--line);
  display: block;
  padding: 12px;
  text-align: right;
  width: 100%;
}

.history-expression {
  color: var(--muted);
  display: block;
  font-size: 0.82rem;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.history-result {
  display: block;
  font-size: 1.15rem;
  font-weight: 760;
  margin-top: 4px;
  overflow-wrap: anywhere;
}

@media (max-width: 760px) {
  .shell {
    grid-template-columns: minmax(0, 1fr);
    padding: 16px;
    place-content: start;
  }

  .history-panel {
    min-height: 220px;
  }
}

@media (max-width: 420px) {
  .calculator,
  .history-panel {
    padding: 14px;
  }

  .keypad {
    gap: 8px;
  }

  .memory-strip {
    grid-template-columns: repeat(4, 1fr);
  }

  .memory-badge {
    grid-column: 1 / -1;
  }
}