html, body {
    margin: 0;
    padding: 0;
  }
        
  canvas,
  .replay-button {
    position: absolute;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    margin: auto;
    z-index: -1;
  }
  
  .replay-button {
    font-size: 24px;
    color: #333;
    width: 200px;
    height: 80px;
    background: white;
    border-radius: 5px;
    border: none;
    z-index: 999999999;
    cursor: pointer;
  }
  
  #start-screen {
    font-family: arial, sans-serif;
    text-align: center;
    display: flex;
    flex-direction: column;
    justify-content: center;
    min-height: 100vh;
    z-index: 99999999;
    background: #ddd;
  }
  
  #start-screen-content {
    background: white;
    margin: 0 auto;
    padding: 20px;
    max-width: 768px;
    border-radius: 5px;
    box-shadow: 0 1px 3px rgba(0,0,0,0.12), 0 1px 2px rgba(0,0,0,0.24);
    transition: all 0.3s cubic-bezier(.25,.8,.25,1);
  }
  
  .flexcontainer {
    display: -webkit-flex;
    display: flex;
    -webkit-flex-direction: column;
    flex-direction: column;
    justify-content: space-between;
  }
  
  .row {
    flex: 1;
    padding: 10px;
  }
  
  .row:not(:last-child) {
    border-bottom: 1px solid lightgrey;
  }
  
  .instructions {
    display: inline-block;
    width: calc(50% - 20px);
  }
  
  #play {
    background: #0dba94;
    color: white;
    margin-top: 10px;
    cursor: pointer;
    font-size: 32px;
    letter-spacing: 2px;
    padding: 20px 60px;
    border: none;
    border-radius: 5px;
  }
  #boostBtn{
    padding:5px;
    background:red;
    color:white;
    position: absolute;
    left:50%;
    display: none;
  }
  /* media query screen-max 600px */
  @media screen and (max-width: 600px) {
 
    #boostBtn{
      display: block;
      top:30%;
    }
  }


  div {
    vertical-align: middle;
  }
  
  h1 {
    font-size: 64px;
    margin: 0;
    padding: 0;
  }
  
  @media (max-width: 600px) {
    .replay-button {
      font-size: 16px;
      height: 60px;
    }
  }