body {
  background: linear-gradient(135deg, #232526 0%, #414345 100%);
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: "Segoe UI", Arial, sans-serif;
  transition: background 0.3s;
}

.calculator-container {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 100vw;
  height: 100vh;
}

.calculator {
  background: #232526;
  border-radius: 20px;
  box-shadow: 0 8px 32px 0 rgba(0, 0, 0, 0.5);
  padding: 30px 25px;
  width: 320px;
  display: flex;
  flex-direction: column;
  gap: 20px;
  transition: background 0.3s, box-shadow 0.3s;
}

.display {
  background: #111;
  color: #74ebd5;
  font-size: 1.3em;
  border-radius: 10px;
  padding: 18px 15px;
  text-align: right;
  margin-bottom: 10px;
  min-height: 50px;
  letter-spacing: 2px;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.08);
  transition: background 0.3s, color 0.3s;
  font-family: "Consolas", "Segoe UI", Arial, sans-serif;
}

.history {
  background: rgba(255, 255, 255, 0.04);
  color: #b8c6db;
  font-size: 1em;
  border-radius: 8px;
  padding: 8px 12px;
  min-height: 24px;
  margin-bottom: 8px;
  text-align: right;
  max-height: 40px;
  overflow-y: auto;
  font-family: "Consolas", "Segoe UI", Arial, sans-serif;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
  margin-top: 8px;
}

.btn {
  background: #333;
  border: none;
  border-radius: 8px;
  font-size: 1.3em;
  padding: 18px 0;
  cursor: pointer;
  transition: background 0.2s, box-shadow 0.2s, color 0.2s;
  box-shadow: 0 2px 6px rgba(0, 0, 0, 0.07);
  font-family: "Segoe UI", Arial, sans-serif;
  font-weight: 500;
  color: #74ebd5;
}

.btn:active {
  background: #222;
}

.btn.equal {
  background: #74ebd5;
  color: #232526;
  grid-row: span 2;
  font-weight: bold;
  font-size: 1.5em;
  border-radius: 12px;
}

.btn.zero {
  grid-column: span 2;
  border-radius: 12px;
}

.btn:hover {
  background: #222;
}