:root {
  --bg: linear-gradient(135deg, #667eea, #764ba2);
  --glass: rgba(255,255,255,0.15);
  --text: #fff;
}

body.dark {
  --bg: linear-gradient(135deg, #0f2027, #203a43);
  --glass: rgba(0,0,0,0.35);
}

* {
  margin: 0;
  box-sizing: border-box;
  font-family: Poppins, sans-serif;
}

body {
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  background: var(--bg);
  transition: background 0.4s ease;
}

.calculator {
  width: 330px;
  padding: 20px;
  border-radius: 20px;
  background: var(--glass);
  backdrop-filter: blur(15px);
  box-shadow: 0 25px 50px rgba(0,0,0,0.3);
  color: var(--text);
}

.top {
  display: flex;
  justify-content: space-between;
  margin-bottom: 10px;
}

.history {
  font-size: 0.9rem;
  opacity: 0.7;
}

.theme-btn {
  background: none;
  border: none;
  font-size: 1.2rem;
  cursor: pointer;
  color: var(--text);
}

#display {
  width: 100%;
  height: 60px;
  border-radius: 12px;
  border: none;
  padding: 10px;
  font-size: 1.8rem;
  text-align: right;
  background: rgba(255,255,255,0.25);
  color: var(--text);
  outline: none;
  margin-bottom: 15px;
}

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

.calc-btn {
  height: 55px;
  border-radius: 12px;
  border: none;
  font-size: 1.1rem;
  background: rgba(255,255,255,0.25);
  color: var(--text);
  cursor: pointer;
  transition: all 0.15s ease;
}

.calc-btn:hover {
  transform: translateY(-2px);
}

.calc-btn:active {
  transform: scale(0.92);
}

.operator {
  background: rgba(255,99,71,0.7);
}

.equals {
  background: rgba(0,255,170,0.8);
  color: #000;
}

.zero {
  grid-column: span 2;
}