.toolbar {
    height: 36px;
    text-align: right;
    line-height: 36px;
    background-color: #fbfbfb;
    padding: 0 20px;
    border-top: #eee 1px solid;
    border-bottom: #eee 1px solid;
    box-sizing: border-box;
}

.flex {
    display: flex;
    flex-direction: row;
    height: calc(100% - 36px);
}
.flex > * {
    width: 50%;
    height: 100%;
}

#content {
    padding: 10px 20px;
    resize: none;
    font-family: monospace;
    font-size: 14px;
    box-sizing: border-box;
}
#content,
#preview {
    border: 0;
}

@media (max-width: 900px) and (orientation: portrait) {
    .flex {
        flex-direction: column;
    }
    .flex > * {
        width: 100%;
        height: 50%;
    }
}