* {
  box-sizing: border-box;
  font-family: system-ui, sans-serif;
}

:root {
  --bg: #e75aba;
  --card: rgba(38, 143, 172, 0.08);
  --display: #831064;
  --text: #e5e7eb;
  --btn: rgba(255,255,255,0.1);
  --op: rgba(18, 18, 18, 0.4);
  --eq: rgba(120, 55, 119, 0.6);
}

body.light {
  --bg: #3d5482;
  --card: rgba(38, 143, 172, 0.08);
  --display: #8abcef;
  --text: #020617;
  --btn: #e5e7eb;
  --op: #c7d2fe;
  --eq: #295098;
}

body {
  min-height: 100vh;
  margin: 0;
  background: linear-gradient(135deg, var(--bg), #0f172a);
  display: flex;
  justify-content: center;
  align-items: center;
}

.calculator-card {
  background: var(--card);
  padding: 20px;
  border-radius: 20px;
  width: 320px;
  box-shadow: 0 10px 30px rgba(0,0,0,0.4);
  color: var(--text);
  transition: 0.3s;
}

.top {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 12px;
}

.theme-btn {
  background: transparent;
  border: none;
  font-size: 20px;
  cursor: pointer;
}



.display {
  background: var(--display);
  padding: 14px;
  border-radius: 12px;
  text-align: right;
  font-size: 28px;
  margin-bottom: 14px;
}

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

button {
  padding: 14px;
  border: none;
  border-radius: 12px;
  background: var(--btn);
  color: var(--text);
  font-size: 18px;
  cursor: pointer;
  transition: transform 0.1s ease, filter 0.1s ease;
}

button:active {
  transform: scale(0.95);
  filter: brightness(1.2);
}

.op {
  background: var(--op);
}

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

.zero {
  grid-column: span 2;
}

.shake {
  animation: shake 0.3s;
}

@keyframes shake {
  0% { transform: translateX(0); }
  25% { transform: translateX(-5px); }
  50% { transform: translateX(5px); }
  75% { transform: translateX(-5px); }
  100% { transform: translateX(0); }
}