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

body {
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
  background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  min-height:100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  padding:20px;
}

.container {
  width:100%;
  max-width:400px;
}

.calculator {
  background:#fff;
  border-radius: 20px;
  box-shadow: 0 20px 60px rgba(0,0,0,0.3);
  padding: 20px;
}

.display {
  background:#222;
  color:#fff;
  font-size: 2.5rem;
  padding: 30px 20px;
  border-radius: 10px;
  text-align: right;
  margin-bottom: 20px;
  min-height:80px;
  word-wrap:break-word;
}

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

.btn{
  padding:25px;
  font-size:1.5rem;
  border:none;
  border-radius: 10px;
  cursor: pointer;
  background: #f0f0f0;
  color: #333;
  transition: all 0.2s;
  font-weight: 600;
}

.btn-hover {
  transform: translateY(-2px);
  box-shadow: 0 5px rgba(0,0,0,0.2);
}

.btn:active {
  transform: translateY(0);
}

.btn-operator {
  background: #667eea;
  color:#fff;
}

.btn-operator:hover {
  background: #5568d3;
}

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

.btn-clear:hover {
  background: #ee5555;
}

.btn-equals {
  background: #51cf66;
  color:#fff;
}

.btn-equals:hover {
  background: #40c057;
}

@media(max-width:480px) {
  .display {
    font-size: 2rem;
    padding: 20px 15px;
  }

  .btn {
    padding: 20px;
    font-size: 1.2rem;
  }
}