* {
  box-sizing: border-box;
  font-family: "Segoe UI", sans-serif;
}

body {
  margin: 0;
  padding: 40px;
  background: linear-gradient(135deg, #d4fc79, #96e6a1);
  display: flex;
  flex-direction: column;
  align-items: center;
  min-height: 100vh;
  transition: background 0.3s ease, color 0.3s ease;
}


body.dark {
  background: linear-gradient(135deg, #2c3e50, #4ca1af);
  color: #fff;
}


.top-controls {
  display: flex;
  gap: 15px;
  margin-bottom: 30px;
}

.top-controls button {
  padding: 12px 24px;
  font-size: 16px;
  font-weight: bold;
  border-radius: 25px;
  border: none;
  cursor: pointer;
  transition: background-color 0.3s ease;
  background-color: #222;
  color: #fff;
}

.top-controls button:hover {
  background-color: #444;
}

.calculator {
  width: 320px;
  background: #ffffff;
  padding: 25px;
  border-radius: 20px;
  box-shadow: 0 10px 30px rgba(0, 0, 0, 0.2);
  transition: all 0.3s ease;
}

.calculator.glass {
  background: rgba(255, 255, 255, 0.15);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border: 1px solid rgba(255, 255, 255, 0.3);
  box-shadow: 0 12px 40px rgba(0, 0, 0, 0.3);
}

body.dark .calculator {
  background: #333;
  color: #fff;
}

body.dark .calculator.glass {
  background: rgba(0, 0, 0, 0.25);
  border: 1px solid rgba(255, 255, 255, 0.2);
}

#display {
  width: 100%;
  height: 55px;
  font-size: 24px;
  text-align: right;
  padding-right: 15px;
  border-radius: 10px;
  border: none;
  margin-bottom: 20px;
  background-color: #f1f1f1;
}

body.dark #display {
  background-color: #222;
  color: #fff;
}

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

button {
  height: 55px;
  font-size: 20px;
  border: none;
  border-radius: 10px;
  background-color: #eee;
  cursor: pointer;
  transition: all 0.2s ease-in-out;
}

button:hover {
  background-color: #ddd;
}

button:active {
  transform: scale(0.95);
}

body.dark .buttons button {
  background-color: #555;
  color: #fff;
}

body.dark .buttons button:hover {
  background-color: #777;
}

.span-two {
  grid-column: span 1;
  background-color: #eee;
  
}


.history-box {
  margin-top: 30px;
  padding: 15px;
  background: #ffffffcc;
  border-radius: 10px;
  box-shadow: 0 4px 10px rgba(0, 0, 0, 0.1);
  width: 300px;
  max-height: 250px;
  overflow-y: auto;
}

.dark .history-box {
  background: #222222cc;
  color: #fff;
}

.history-box h3 {
  margin-top: 0;
  font-size: 20px;
}

#history-list {
  list-style: none;
  padding: 0;
  margin: 0;
}

#history-list li {
  padding: 5px 0;
  border-bottom: 1px solid #ddd;
  font-size: 16px;
}

#clear-history {
  margin-top: 10px;
  padding: 6px 12px;
  font-size: 14px;
  background-color: #ff6666;
  color: white;
  border: none;
  border-radius: 6px;
  cursor: pointer;
}

#clear-history:hover {
  background-color: #e14c4c;
}