body {
  background-color: #f9f9e5;
  padding: 30px 0;
}

.js-calculator {
  padding: 8px;
  margin: 0 auto;
  width: 270px;
  background-color: #ccc;
  font-size: 21px;
  transition: ease-in 0.5s;
  box-shadow: 2px 2px 2px #999;
  border-radius: 5px;
}
.js-calculator::after {
  content: "";
  display: table;
  clear: both;
}
.js-calculator.rotate {
  transform: rotate(180deg);
}
.js-calculator .logo {
  box-sizing: border-box;
  padding: 2px;
  font-size: 14px;
  text-align: center;
  font-family: "Rationale", "Courier New";
  color: #666;
}
.js-calculator .logo a {
  display: inline-block;
  margin-left: 3px;
  font-family: "Kalam", cursive;
  color: #666;
  text-decoration: none;
}
.js-calculator .logo a:hover {
  opacity: 0.7;
}
.js-calculator .display {
  box-sizing: border-box;
  background-color: #000;
  font-family: "Rationale", "Courier New", sans-serif;
}
.js-calculator .display .main {
  font-size: 40px;
  box-sizing: border-box;
  height: auto2em;
  padding-top: 0.4em;
  padding-right: 0.2em;
  color: lime;
  text-align: right;
  overflow: hidden;
}
.js-calculator .display .history {
  font-size: 18px;
  box-sizing: border-box;
  padding-bottom: 0.25em;
  padding-right: 0.5em;
  color: gray;
  text-align: right;
  overflow: hidden;
}
.js-calculator .buttons {
  margin-top: 5px;
}
.js-calculator .btn {
  box-sizing: border-box;
  float: left;
  width: 25%;
  height: 50px;
  background-color: #fff;
  font-family: "Audiowide", "Courier New", sans-serif;
  font-size: 26px;
  outline: none;
  border-radius: 6px;
}
.js-calculator .btn:hover {
  background-color: #e2e2e2;
}
.js-calculator .btn.operator {
  background-color: orange;
}
.js-calculator .btn.operator:hover {
  background-color: red;
}
.js-calculator .blank {
  float: left;
  width: 25%;
  height: 50px;
}

code {
  background-color: #eee;
  border: 1px solid #999;
  display: block;
  padding: 2%;
  margin-top: 20px;
}