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

html,body{
width: 100%;
height: 100%;
}

* {
  box-sizing: border-box;
}

body {
  font-family: 'Poppins', sans-serif;
  background: linear-gradient(135deg, #89f7fe, #66a6ff);
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  margin: 0;
}

.calculator {
  background: #1e1e1e;
  width: 320px;
  border-radius: 20px;
  box-shadow: 0 8px 25px rgba(0,0,0,0.3);
  padding: 20px;
}

.display {
  background: #333;
  color: #fff;
  text-align: right;
  padding: 20px;
  border-radius: 10px;
  font-size: 2em;
  overflow: hidden;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
  margin-top: 20px;
}

.btn {
  background: #505050;
  color: white;
  font-size: 1.3em;
  border: none;
  border-radius: 12px;
  padding: 15px;
  cursor: pointer;
  transition: background 0.2s;
}

.btn:hover {
  background: #6b6b6b;
}

.btn.clear {
  background: #ff5c5c;
}

.btn.clear:hover {
  background: #ff3b3b;
}

.btn.equal {
  background: #4cd964;
  grid-column: span 1;
}

.btn.equal:hover {
  background: #3dc25e;
}

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