main.css

html,body{
    margin: 0;
    padding: 0;
    font-family: Arial, Helvetica, sans-serif;
    font-size: 18px;
  }

  body{
    background: #AAFFA9;  /* fallback for old browsers */
    background: -webkit-linear-gradient(to right, #11FFBD, #AAFFA9);  /* Chrome 10-25, Safari 5.1-6 */
    background: linear-gradient(to right, #11FFBD, #AAFFA9); /* W3C, IE 10+/ Edge, Firefox 16+, Chrome 26+, Opera 12+, Safari 7+ */
  }

  a {
    text-decoration: none;
  }

  main{
      height: 100vh;
  }

  main > .wrapper{
      padding: 20px;
      background-color: rgba(255,255,255,.5);
      border-radius: 10px;
  }

  kbd {
    display: inline-block;
    vertical-align: top;
    text-transform: uppercase;
    position: relative;
  }

  kbd > .button{
      position: absolute;
      right: -2px;
      bottom: 0;
      border: none;
      border-radius: 3px;
      transform: scale(0.8);
      background-color: rgb(17, 100, 65);
      padding: 0;
      color: #c5c5c5;
      display: none;
  }

  kbd:hover > button{
      display: inline-block;
  }

  main {
    text-align: center;
    display: flex;
    justify-content: center;
    align-items: center;
  }

  main div:nth-child(3) {
    margin-left: -70px;
  }

  .key{
    width: 50px;
    height: 40px;
    background-image: linear-gradient(to bottom,#292929 0%,#111111 100%);
    border: 1px solid #373737;
    color: #c5c5c5;
    border-radius: 6px;
    box-shadow: 0 0 0 1px #1a1b1c,0 0 0 1px #1f2020,0 3px 0 1px #080808;  
    margin: 10px 10px;
    position: relative;
  }

  .key img{
      width: 16px;
      height: 16px;
      position: absolute;
      left: 4px;
      bottom: 2px;
  }

  .key .text{
    position: absolute;
    left: 0;
    left: 4px;
  }