body {
    background-color: gray;
    margin: 0;
    padding: 0;
    }

  .container {
    positon:relative;
    color: white;
    font-family: Arial;
    font-size: 12px;
    }

  .container .center {
    height: 80%;
    left: 50%;
    position: absolute;
    top: 50%;
    transform: translate(-50%, -50%);
    width: 90%;
    }

  .container .header {
    font-weight: bold;
    padding: 1em 0 1em 0;
    }

  #myContainer {
    border: 1px solid lightgray;
    height: 100%;
    }