body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background: #f0f4f8;
  font-family: "Segoe UI", sans-serif;
  margin: 0;
}

.calculator-container {
  display: flex;
  justify-content: center;
  align-items: center;
}

.calculator {
  background: #ffffff;
  padding: 30px 25px;
  border-radius: 20px;
  box-shadow: 0 15px 40px rgba(0,0,0,0.1);
  width: min(90vw, 320px);
  display: flex;
  flex-direction: column;
  align-items: center;
}

.display {
  width: 100%;
  height: 60px;
  background: #e5e7eb;
  border: none;
  border-radius: 12px;
  text-align: right;
  font-size: 28px;
  padding: 0 15px;
  margin-bottom: 25px;
  color: #1f1f1f;
  box-sizing: border-box;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 15px;
  width: 100%;
}

.btn {
  padding: 18px 0;
  font-size: 20px;
  border: none;
  border-radius: 12px;
  background: #f0f0f0;
  cursor: pointer;
  transition: transform 0.2s, background 0.2s;
  width: 100%;
  box-sizing: border-box;
}

.btn:hover {
  transform: scale(1.05);
  background: #60a5fa;
  color: #fff;
}

.equal {
  grid-row: span 2;
  background: #3b82f6;
  color: white;
}

.clear {
  background: #f87171;
  color: white;
}

/* Optional: Different color for operators */
.btn[data-value="+"],
.btn[data-value="-"],
.btn[data-value="*"],
.btn[data-value="/"] {
  background: #60a5fa;
  color: white;
}

.btn[data-value="+"]:hover,
.btn[data-value="-"]:hover,
.btn[data-value="*"]:hover,
.btn[data-value="/"]:hover {
  background: #2563eb;
}