estilos.css

body {
    margin: 0;
    background: #fafafa;
    display: flex;
    align-items: center;
    height: 100vh;
  }

  .gameboard {
    height: 100vh;
    width: 100vh;
    border-radius: 50%;
    overflow: hidden;
    margin: 0 auto;
    max-height: 60vh;
    max-width: 60vh;
  }

  .color {
    width: 50%;
    height: 50%;
    display: inline-block;
  }

  .izquierda {
    float: left;
  }

  .derecha {
    float: left;
  }

  .azul {
    background: #ffdd57;
  }

  .azul.light {
    background: #ffeeab;
  }

  .morado {
    background: #3273dc;
  }

  .morado.light {
    background: #99b9ee;
  }

  .naranja {
    background: #f14668;
  }

  .naranja.light {
    background: #f8a3b4;
  }

  .verde {
    background: #48c774;
  }

  .verde.light {
    background: #a4e3ba;
  }

  .btn-start {
    width: 400px;
    height: 100px;
  
    font-family: inherit;
    font-size: 2.5rem;
    padding: 0.5em 1em;
    color: #ffffff;
    border: none rgba(0, 0, 0, 0);
    background-color: #00d1b2;
    text-decoration: none;
    border-radius: 6px;
    border: 4px solid #fff; /* Green */

    position: absolute;
    top: calc(50% - 50px);
    left: calc(50% - 200px);
  }

  .btn-start-hover,
  .btn-start:hover,
  .btn-start:focus {
      background-image: linear-gradient(transparent, rgba(0,0,0, 0.05) 40%, rgba(0,0,0, 0.10));
  }

  .hide {
    display: none;
  }