* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html, body {
  height: 100vh;
  width: 100%;
  background: linear-gradient(135deg, #141e30, #243b55);
  font-family: 'Segoe UI', sans-serif;
  display: flex;
  justify-content: center;
  align-items: center;
}

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

.calculator {
  backdrop-filter: blur(20px);
  background: rgba(255, 255, 255, 0.07);
  border-radius: 30px;
  padding: 25px;
  box-shadow: 0 8px 40px rgba(0, 0, 0, 0.4);
  width: 380px;
  max-width: 90%;
}

#display {
  width: 100%;
  height: 60px;
  border: none;
  border-radius: 15px;
  background: rgba(255, 255, 255, 0.15);
  font-size: 28px;
  font-weight: bold;
  text-align: right;
  padding: 12px;
  color: #fff;
  margin-bottom: 25px;
  box-shadow: inset 0 2px 6px rgba(0, 0, 0, 0.2);
}

.buttons {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 15px;
}

.btn {
  height: 65px;
  border: none;
  border-radius: 15px;
  font-size: 22px;
  font-weight: bold;
  color: #fff;
  background: rgba(255, 255, 255, 0.1);
  cursor: pointer;
  transition: all 0.2s ease;
  backdrop-filter: blur(10px);
}

.btn:hover {
  background: rgba(255, 255, 255, 0.2);
  transform: scale(1.05);
}

.btn:active {
  background: rgba(255, 255, 255, 0.3);
}

.operator {
  background: rgba(255, 165, 0, 0.7);
}

.operator:hover {
  background: rgba(255, 165, 0, 0.9);
}

.operator:active {
  background: rgba(255, 165, 0, 1);
}

.history {
  margin-top: 20px;
  max-height: 140px;
  overflow-y: auto;
  padding: 10px;
  background: rgba(255, 255, 255, 0.08);
  border-radius: 12px;
  color: #fff;
}

.history h3 {
  margin-bottom: 10px;
  font-size: 18px;
  border-bottom: 1px solid rgba(255,255,255,0.3);
  padding-bottom: 5px;
}

#history-list {
  list-style: none;
  font-size: 16px;
}

#history-list li {
  margin-bottom: 6px;
  padding: 6px;
  border-radius: 8px;
  cursor: pointer;
  transition: 0.2s ease-in-out;
}

#history-list li:hover {
  background-color: rgba(255, 255, 255, 0.2);
}