/* Global Reset */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
body {
  font-family: 'Inter', sans-serif;
  background: #0d1117;
  color: #f5f5f5;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 100vh;
}

/* Calculator Container */
.calculator-container {
  display: flex;
  align-items: center;
  justify-content: center;
  margin-top: 40px;
}
.calculator {
  background: #1f2937;
  padding: 20px;
  border-radius: 16px;
  box-shadow: 0 10px 30px rgba(0,0,0,0.6);
}

/* Display Screen */
.display input {
  width: 100%;
  height: 70px;
  border: none;
  border-radius: 10px;
  background: #111827;
  color: #f5f5f5;
  font-size: 2rem;
  padding: 15px;
  text-align: right;
  outline: none;
  box-shadow: inset 0 0 10px rgba(0,0,0,0.6);
}

/* Buttons Grid */
.buttons {
  display: grid;
  grid-template-columns: repeat(4, 80px);
  grid-gap: 15px;
  margin-top: 20px;
}
.btn {
  height: 70px;
  border: none;
  border-radius: 10px;
  background: #374151;
  color: #f5f5f5;
  font-size: 1.3rem;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.2s ease, transform 0.1s ease;
}
.btn:hover {
  background: #4b5563;
}
.btn:active {
  transform: scale(0.95);
}

/* Special Buttons */
.operator {
  background: #3b82f6;
  color: #fff;
}
.operator:hover {
  background: #2563eb;
}
.equal {
  background: #8b5cf6;
  color: #fff;
  grid-column: span 2; /* make = button larger */
}
.equal:hover {
  background: #7c3aed;
}
.clear {
  background: #ef4444;
  color: #fff;
}
.clear:hover {
  background: #dc2626;
}
.backspace {
  background: #f59e0b;
  color: #fff;
}
.backspace:hover {
  background: #d97706;
}

/* Footer */
footer {
  margin-top: 40px;
  background: #111827;
  padding: 15px;
  width: 100%;
  text-align: center;
  color: #9ca3af;
  font-size: 0.9rem;
}