style.css

body {
    background: #636e72;
  }

  #main {
    width: 245px;
    height: 300px;
    margin: 0 auto;
    margin-top:20vh;
  }

  #result {
    background: #2c3e50;
    width: 100%;
    height: 60px;
    overflow: hidden;
  }

  #resultInner {
    display: block;
    background: #fff;
    width: 225px;
    height: 40px;
    margin: 10px;
    color: #000;
    font-size:30px;
  }

  #numbers {
    background: #bdc3c7;
    width: 185px;
    height: 235px;
    float: left;
  }

  #numbers .num {
    width: 50px;
    height: 50px;
    font-weight: bolder;
    margin: 4px;
  }

  #operators {
    background: #95a5a6;
    width: 60px;
    height: 235px;
    float: right
  }

  #operators .operator {
    width: 50px;
    height: 50px;
    font-weight: bolder;
    margin: 4px;
  }

  #resultOperators {
    background: #7f8c8d;
  }

  #resultOperators .resultOperator {
    width: 50px;
    height: 50px;
    font-weight: bolder;
    margin: 4px;
  }

  .clear {
    clear: both;
  }

  #equation {
    width: 173px !important;
  }
  h1{
    font-weight: bolder;
    font-family: sans-serif;
    font-size:1.9rem;
    color:#FFD365;
  }