* {
  box-sizing: border-box;
  font-family: "Inter", system-ui, sans-serif;
}

body {
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  background: radial-gradient(circle at top, #1e293b, #020617);
}

.calculator {
  background: rgba(15, 23, 42, 0.85);
  backdrop-filter: blur(12px);
  padding: 22px;
  border-radius: 18px;
  width: 300px;
  box-shadow:
    0 25px 50px rgba(0, 0, 0, 0.5),
    inset 0 1px rgba(255, 255, 255, 0.05);
}
.title {
  text-align: center;
  margin-bottom: 16px;
  font-size: 1.35rem;
  font-weight: 700;
  color: #f8fafc;
  letter-spacing: 0.06em;
}
.title::after {
  content: "";
  display: block;
  width: 96px;   /* increased length */
  height: 3px;   /* slightly thicker */
  background: #3b82f6;
  margin: 10px auto 0;
  border-radius: 3px;
}




#display {
  width: 100%;
  height: 64px;
  margin-bottom: 18px;
  font-size: 1.9rem;
  text-align: right;
  padding: 14px;
  border: none;
  border-radius: 12px;
  background: #020617;
  color: #f8fafc;
  box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.06);
}

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

button {
  height: 56px;
  border: none;
  border-radius: 14px;
  font-size: 1.15rem;
  cursor: pointer;
  background: linear-gradient(180deg, #1e293b, #0f172a);
  color: #e5e7eb;
  box-shadow:
    0 6px 14px rgba(0, 0, 0, 0.4),
    inset 0 1px rgba(255, 255, 255, 0.06);
  transition: transform 0.08s ease, box-shadow 0.08s ease, filter 0.08s;
}

button:hover {
  filter: brightness(1.15);
}

button:active {
  transform: translateY(2px);
  box-shadow:
    0 3px 8px rgba(0, 0, 0, 0.45),
    inset 0 1px rgba(255, 255, 255, 0.04);
}

.operator {
  background: linear-gradient(180deg, #3b82f6, #1d4ed8);
  color: #fff;
}

.equals {
  grid-row: span 2;
  background: linear-gradient(180deg, #22c55e, #16a34a);
  color: #022c22;
  font-weight: 600;
}

.clear {
  background: linear-gradient(180deg, #ef4444, #b91c1c);
  color: #fff;
}

.zero {
  grid-column: span 2;
}