:root {
  --bg: #101522;
  --panel: #1a2133;
  --text: #f4f7ff;
  --muted: #9aa3bf;
  --accent: #6e8bff;
  --accent-dark: #4b6af2;
  --operator: #f08b28;
  --operator-dark: #d67216;
  --danger: #d14e5a;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: "Inter", "Segoe UI", Arial, sans-serif;
  background: radial-gradient(circle at top, #1f2a44, var(--bg) 50%);
  color: var(--text);
  display: grid;
  place-items: center;
  padding: 20px;
}

.app-shell {
  width: min(940px, 100%);
  display: grid;
  grid-template-columns: minmax(320px, 1fr) minmax(240px, 280px);
  gap: 18px;
}

.calculator,
.history-panel {
  background: linear-gradient(160deg, rgba(255, 255, 255, 0.08), rgba(255, 255, 255, 0.02));
  border: 1px solid rgba(255, 255, 255, 0.1);
  border-radius: 18px;
  backdrop-filter: blur(10px);
}

.calculator {
  padding: 20px;
}

.calculator-header h1 {
  margin: 0;
  font-size: 1.6rem;
}

.calculator-header p {
  margin: 6px 0 16px;
  color: var(--muted);
  font-size: 0.95rem;
}

.display-wrap {
  background: rgba(0, 0, 0, 0.26);
  border: 1px solid rgba(255, 255, 255, 0.08);
  border-radius: 14px;
  padding: 12px;
  margin-bottom: 16px;
}

.expression {
  height: 24px;
  color: var(--muted);
  text-align: right;
  font-size: 0.95rem;
  overflow: hidden;
}

.display {
  width: 100%;
  background: transparent;
  border: none;
  color: var(--text);
  text-align: right;
  font-size: 2rem;
  font-weight: 700;
}

.display:focus {
  outline: none;
}

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

.btn {
  border: none;
  border-radius: 12px;
  padding: 14px;
  color: var(--text);
  background: rgba(255, 255, 255, 0.08);
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: transform 0.1s ease, background-color 0.2s ease;
}

.btn:hover {
  background: rgba(255, 255, 255, 0.14);
}

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

.btn-operator {
  background: var(--operator);
}

.btn-operator:hover {
  background: var(--operator-dark);
}

.btn-equal {
  background: var(--accent);
  grid-row: span 2;
}

.btn-equal:hover {
  background: var(--accent-dark);
}

.btn-fn,
.btn-muted,
.btn-memory {
  color: #dde3f5;
}

.memory-controls {
  margin-top: 12px;
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
}

.history-panel {
  padding: 18px;
  display: flex;
  flex-direction: column;
  min-height: 220px;
}

.history-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 8px;
}

.history-header h2 {
  margin: 0;
  font-size: 1.1rem;
}

.small {
  padding: 8px 12px;
  font-size: 0.85rem;
}

#history-list {
  list-style: none;
  margin: 0;
  padding: 0;
  overflow-y: auto;
  display: flex;
  flex-direction: column;
  gap: 8px;
}

#history-list li {
  background: rgba(255, 255, 255, 0.05);
  border: 1px solid rgba(255, 255, 255, 0.08);
  border-radius: 10px;
  padding: 8px 10px;
  color: #eaf0ff;
  font-size: 0.92rem;
}

#history-list .empty {
  color: var(--muted);
  text-align: center;
}

@media (max-width: 800px) {
  .app-shell {
    grid-template-columns: 1fr;
  }
}