#demo_container {
    display: flex;
    flex-direction: column;
    align-items: center;

}

#canvas_container {
    max-width: 640px;
    width: 100%;
}

#canvas_container>canvas {
    border: .1rem solid blue;
    padding: .5rem;
}

#demo_container form {
    display: grid;
    grid-template-columns: 1fr 1fr;
    justify-items: start;
    max-width: 22rem;
    border: .1rem solid blue;
    padding: .5rem;
    grid-row-gap: 1rem;
    margin: 1rem;
}

#demo_container form label {
    grid-column-start: span 2;
}

#demo_container button {
    grid-row: span 2;
}

#demo_container output {
    justify-self: center;
}

/* expand for larger screens */
@media screen and (min-width: 475px) {
    #demo_container form {
        max-width: 25rem;
        grid-template-columns:
            10rem 10rem 5rem;
    }

    #demo_container form label {
        grid-column-start: span 1;
    }
}