* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: "SF Pro Display", sans-serif;
  user-select: none;
  -webkit-tap-highlight-color: transparent;
}

body {
  background: #0d0d0d;
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
}

.calculator {
  width: 350px;
  background: #1c1c1e;
  padding: 20px;
  border-radius: 25px;
  box-shadow: 0 0 30px rgba(0, 0, 0, 0.6);
}

.display {
  background: #000;
  padding: 25px 15px;
  border-radius: 15px;
  text-align: right;
  margin-bottom: 20px;
  overflow: hidden;
}

.output {
  color: #fff;
  font-size: 3rem;
  font-weight: 300;
}

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

.btn {
  background: #2c2c2e;
  border: none;
  color: #fff;
  font-size: 1.4rem;
  padding: 22px;
  border-radius: 50%;
  cursor: pointer;
  transition: all 0.15s ease;
  user-select: none;
}

.operator {
  background: #ff9f0a;
  color: #fff;
  font-weight: bold;
}

.clear {
  background: #a5a5a5;
  color: white;
  font-weight: bold;
}

.equal {
  background: #30d158;
  color: #fff;
  font-weight: bold;
}

.btn:hover {
  filter: brightness(1.2);
}

.btn:active {
  transform: scale(0.93);
}