body {
  font-family: Arial, sans-serif;
  display: flex;
  justify-content: center;
  padding: 20px;
}

#calculator {
  border: 2px solid #333;
  padding: 10px;
  width: 300px;
}

#display {
  width: 100%;
  height: 40px;
  font-size: 1.5em;
  margin-bottom: 10px;
  text-align: right;
  padding-right: 10px;
}

#buttons button {
  width: 22%;
  height: 40px;
  margin: 3px 1%;
  font-size: 1.2em;
}

#history-list {
  margin-top: 10px;
  list-style-type: none;
  padding-left: 0;
  max-height: 150px;
  overflow-y: auto;
  border-top: 1px solid #ccc;
}