* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background: #a8d8ea;
  font-family: 'Segoe UI', sans-serif;
}

.calculator {
  background: #1e1e2e;
  border-radius: 20px;
  padding: 24px;
  box-shadow: 0 20px 60px rgba(0, 0, 0, 0.5);
  width: 320px;
}

.display {
  background: #13131f;
  border-radius: 12px;
  padding: 16px 20px;
  margin-bottom: 20px;
  min-height: 90px;
  display: flex;
  flex-direction: column;
  align-items: flex-end;
  justify-content: flex-end;
  gap: 6px;
}

.expression {
  color: #666;
  font-size: 14px;
  min-height: 20px;
  word-break: break-all;
}

.result {
  color: #fff;
  font-size: 36px;
  font-weight: 300;
  word-break: break-all;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
}

.btn {
  background: #2a2a3e;
  color: #fff;
  border: none;
  border-radius: 12px;
  padding: 18px;
  font-size: 18px;
  cursor: pointer;
  transition: background 0.15s, transform 0.1s;
}

.btn:hover {
  background: #3a3a52;
}

.btn:active {
  transform: scale(0.95);
  background: #4a4a62;
}

.btn-clear {
  background: #3d2a2a;
  color: #ff6b6b;
}

.btn-clear:hover {
  background: #4e3535;
}

.btn-operator {
  background: #2a3d52;
  color: #60b4ff;
}

.btn-operator:hover {
  background: #354d66;
}

.btn-equals {
  background: #4361ee;
  color: #fff;
}

.btn-equals:hover {
  background: #5472f5;
}

.btn-zero {
  grid-column: span 2;
}