style.css

p {
    font-size: 1.1rem;
}

mark {
    color: #e83e8c;
    word-break: break-word;
}

.block {
    position: relative;
    padding: 1rem;
    border: solid #f7f7f9;
    /*background: #fafafa;*/
}

.output {
    display: block;
    height: 6.7em;
    width: 100%;
    /*padding: 0.6rem;*/
    border: 1px solid transparent;
}

pre {
    background: #fafafa;
}

.filler {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
}


/* Visualization component
   ------------------------- */
.visualization { height: 100%; }
/* Layout */
.visualization__color-list {
    text-align: left;
}
.visualization__color-picker {
    position: absolute;
    left: 25px;
}
.visualization__rectangle {
    height: 200px;
    width: 200px;
    margin: 60px auto;
}
.visualization__style-list {
    padding: 1rem;
    width: 100%;
    display: flex;
    flex-flow: wrap;
    justify-content: center;
}
/* Elements */
.visualization__color {
    cursor: pointer;
    display: inline-block;
    height: 25px;
    width: 25px;
    background: transparent;
    border: 2px solid #f7f7f9;
}
.visualization__color:hover, .visualization__color.is-active {
    border: 2px solid #80bdff;
}
.visualization__style {
    padding: 1rem;
    margin: 0 10px 1rem;
    background: unset;
    border: none;
}