:root {
  --bg-color: #f4f4f4;
  --text-color: #222;
  --btn-bg: #e0e0e0;
  --btn-hover: #d4d4d4;
  --accent-color: #ff9500;
}
body.dark {
  --bg-color: #1e1e1e;
  --text-color: #f8f8f8;
  --btn-bg: #333;
  --btn-hover: #444;
  --accent-color: #26c281;
}
body {
  background-color: var(--bg-color);
  font-family: 'Segoe UI', Arial, sans-serif;
  display: flex;
  flex-direction: column;
  align-items: center;
  min-height: 100vh;
  margin: 0;
  padding: 40px 0;
  color: var(--text-color);
  transition: background-color 0.3s, color 0.3s;
}
.top-bar {
  width: 320px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 10px;
}
.calculator {
  background: var(--btn-bg);
  border-radius: 15px;
  width: 320px;
  padding: 20px;
  box-shadow: 0 0 20px rgba(0,0,0,0.15);
}
#display {
  width: 100%;
  height: 60px;
  font-size: 28px;
  text-align: right;
  border: none;
  border-radius: 10px;
  margin-bottom: 15px;
  padding-right: 10px;
  background-color: var(--bg-color);
  color: var(--text-color);
}
.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
}
button {
  height: 60px;
  font-size: 20px;
  border: none;
  border-radius: 8px;
  background-color: var(--btn-bg);
  color: var(--text-color);
  cursor: pointer;
  transition: background-color 0.2s;
}
button:hover {
  background-color: var(--btn-hover);
}
button.accent {
  background-color: var(--accent-color);
  color: #fff;
}
.history {
  margin-top: 20px;
  width: 320px;
  max-height: 150px;
  overflow-y: auto;
  background-color: var(--btn-bg);
  border-radius: 10px;
  padding: 10px;
}
.history-item {
  display: flex;
  justify-content: space-between;
  margin-bottom: 5px;
  font-size: 16px;
}