html, body { height: 100%; padding: 0; margin: 0;}

#canvas {
    background: url('./images/wand.jpg');
    max-height: 100%;
    max-width: 100%;
    background-size:     cover;
    background-repeat:   no-repeat;
    background-position: center center;
    float: left;
}

.control_panel {
    float: left;
    border: 1px solid black;
    height: 10em;
    display: block;
    margin-left: 1em;
}

input:invalid {
  border: red solid 3px;
}