body {
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  background: radial-gradient(1200px 800px at 10% 10%, rgba(124,92,255,0.25), transparent 50%),
              radial-gradient(1000px 700px at 90% 20%, rgba(34,211,238,0.18), transparent 55%),
              #0f172a; /* fallback background (deep slate color) */
  color: #ffffff;
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}


.calculator {
  background: rgba(255, 255, 255, 0.15);
  backdrop-filter: blur(12px);
  border-radius: 20px;
  padding: 20px;
  box-shadow: 0 8px 25px rgba(0, 0, 0, 0.2);
  width: 300px;
}

#display {
  width: 100%;
  height: 60px;
  border: none;
  border-radius: 10px;
  margin-bottom: 20px;
  padding: 0 15px;      /* tighter padding */
  font-size: 28px;      /* slightly larger font */
  line-height: 60px;    /* vertically centered text */
  text-align: right;    /* numbers stay aligned right */
  background: rgba(255, 255, 255, 0.25);
  color: #fff;
  outline: none;
  box-sizing: border-box; /* ensures padding doesn't break layout */
}

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

.btn {
  background: rgba(255, 255, 255, 0.2);
  border: none;
  border-radius: 12px;
  padding: 18px;
  font-size: 20px;
  color: #fff;
  cursor: pointer;
  transition: 0.2s;
}

.btn:hover {
  background: rgba(255, 255, 255, 0.35);
}

.operator {
  background: rgba(255, 165, 0, 0.6);
}

.operator:hover {
  background: rgba(255, 165, 0, 0.8);
}

.equals {
  grid-column: span 1;
  background: rgba(0, 200, 83, 0.6);
}

.equals:hover {
  background: rgba(0, 200, 83, 0.8);
}

.zero {
  grid-column: span 2;
}