style.css

* {
    box-sizing: border-box;
}
html, body {
    width: 100%;
    height: 100%;
}

#test-container {
    display: flex;
}
#test-container > * {
    width: 50%;
    flex: 1 1 auto;
    margin: 0 10px;
}
@media (max-width: 767px) {
    #vdom-col {
        display: none;
    }
}
.toolbar {
    height: 35px;
    visibility: hidden;
    background: #222222;
    color: white;
}
.toolbar div.btn {
    box-sizing: content-box;
    display: inline-block;
    padding: 7px;
}
.toolbar div.active {
    background: #555555;
}

#dom {
    min-height: 500px;
    padding: 5px;
}
span.btn {
    display: inline-block;
    background-color: blue;
    padding: 15px;
    color: white;
}
.mr8 {
    margin-right: 16px;
}
td {
    border: 1px solid grey;
    padding: 6px;
}