body {
  font-family: helvetica, arial, sans-serif;
  font-weight: 300;
  margin: 0;
  background: #f6f3ee;
}

.calculator {
  width: 100%;
  max-width: 480px;
  height: 100vh;
  max-height: 640px;
  margin: auto;
}

.keys {
  position: fixed;
  bottom: 0;
  left: 0;
  width: 100%;
}

.keys .key {
  font-size: 30px;
  line-height: 90px;
  float: left;
  -webkit-box-sizing: border-box;
          box-sizing: border-box;
  width: calc(100% / 3);
  height: 90px;
  text-align: center;
  color: #fafafa;
  border: 1px solid #f0f0f0;
  border-radius: 15px;
  background: #81a0aa;
}

.keys .key:last-child {
  width: calc(100% / 3 * 2);
}

.keys .key:active {
  font-weight: bold;
  color: #29558c;
  background-color: #ffa05a;
}

.base {
  font-size: 20px;
  line-height: 60px;
  position: fixed;
  top: 0;
  left: 0;
  -webkit-box-sizing: border-box;
          box-sizing: border-box;
  width: 100%;
  height: 62px;
  padding-left: 10px;
  color: #fff;
  background: #81a0aa;
}

.base .change {
  font-size: 16px;
  font-weight: bold;
  line-height: 50px;
  position: fixed;
  top: 5px;
  right: 10px;
  display: inline-block;
  height: 50px;
  padding: 0 15px;
  color: #f6f3ee;
  border: 1px solid #f6f3ee;
  border-radius: 15px;
}

.base .change.active {
  border: 1px solid #ffa05a;
  background: #ffa05a;
}

.input {
  font-size: 40px;
  position: fixed;
  bottom: 520px;
  left: 0;
  width: 96%;
  padding-right: 4%;
  text-align: right;
  color: #81a0aa;
}

.output {
  font-size: 70px;
  position: fixed;
  bottom: 400px;
  left: 0;
  width: 96%;
  padding-right: 4%;
  text-align: right;
  color: #29558c;
}