JS/HTML/CSS: dividing one CSS class into several classes


This Content is from Stack Overflow. Question asked by Ben123

I am extending this HTML5 image editor repo (repo: https://github.com/viliusle/miniPaint, live version: https://github.com/viliusle/miniPaint).

I want to separate the tools on the left into different sections with a gap between them (see attached picture circled in red). I want each different set of tools in each section to have unique CSS properties (e.g. when I hover over or click on one of the first three tools, the background color (green in picture), should be different).

Desired effect:

Effect so far:

As you can see I’m quite far away from the desired effect and my solution (as code below shows) is very inelegant/hacky. I can’t seem to get past this.

This is the javascript function which renders the tools (I have labelled what I have done so far with ‘My Extension’):

render_tools() {
        var target_id = "tools_container";
        var _this = this;
        var saved_tool = this.Helper.getCookie('active_tool');
        if(saved_tool == 'media' || saved_tool == 'shape' || saved_tool == 'inpaint' || saved_tool == 'imagine' || saved_tool == 'variation') {
            //bringing this back by default gives bad UX
            saved_tool = null
        if (saved_tool != null) {
            this.active_tool = saved_tool;

        //left menu
        for (var i in config.TOOLS) {
            var item = config.TOOLS[i]; //config.TOOLS is a list of tools defined elsewhere
//My extension starts

            if(i == 3) {
                var emptyDom = document.createElement('span');
                emptyDom.className = 'item empty_box';
//My extension ends

                var title = item.title;
                var title = this.Helper.ucfirst(item.name).replace(/_/, ' ');

            var itemDom = document.createElement('span');
            itemDom.id = item.name;
            itemDom.title = title;
            if (item.name == this.active_tool) {
                itemDom.className = 'item trn active ' + item.name;
            else {
                itemDom.className = 'item trn ' + item.name;
            if(item.visible === false){
                itemDom.style.display = 'none';

            itemDom.addEventListener('click', function (event) {


        new app.Actions.Activate_tool_action(this.active_tool, true).do();

And the relevant bits of the css file (with my extension labelled):

/* ========== left sidebar ================================================== */

    -ms-grid-row: 2;
    -ms-grid-column: 1;
    grid-area: sidebar_left;
    display: flex;
    flex-direction: row;
    flex-wrap: wrap;
    background-color: var(--section-background-color);
    padding: 0 5px 5px 0;
    margin-right: 5px;
    overflow: hidden;
    align-self: start;
    width: 40px;
    overflow-y: auto;
    max-height: 100%;
//My extension

.sidebar_left .empty_box:after{
    position: absolute;
    content: '';
    background-position: center center;
    background-repeat: no-repeat;
    background-size: 20px 20px;
    cursor: default
//My extension ends

.sidebar_left .item{
    position: relative;
    background-color: var(--area-background-color);
    height: 25px;
    width: 30px;
    margin: 5px 0 0 5px;
    overflow: hidden;
    cursor: pointer;
.sidebar_left .item:after{
    position: absolute;
    content: '';
    filter: var(--menu-icons-filter);
    background-position: center center;
    background-repeat: no-repeat;
    background-size: 20px 20px;
.sidebar_left .item:hover{
    background-color: var(--background-color-hover);
.sidebar_left .item.active{
    background-color: var(--background-color-active);
    color: var(--text-color-active);
.sidebar_left .item.active:after{
    filter: var(--menu-icons-filter-active);

.sidebar_left .select:after{ background-image: url('images/icons/select.svg'); }
.sidebar_left .selection:after{ background-image: url('images/icons/selection.svg'); }
.sidebar_left .brush:after{ background-image: url('images/icons/brush.svg'); }
.sidebar_left .pencil:after{ background-image: url('images/icons/pencil.svg'); }
.sidebar_left .pick_color:after{ background-image: url('images/icons/pick_color.svg'); }
.sidebar_left .erase:after{ background-image: url('images/icons/erase.svg'); }
.sidebar_left .magic_erase:after{ background-image: url('images/icons/magic_erase.svg'); }
.sidebar_left .fill:after{ background-image: url('images/icons/fill.svg'); }
.sidebar_left .media:after{ background-image: url('images/icons/media.svg'); }
.sidebar_left .shape:after{ background-image: url('images/icons/shape.svg'); }
.sidebar_left .variation:after{ background-image: url('images/icons/variation.svg'); }
.sidebar_left .imagine:after{ background-image: url('images/icons/imagine.svg'); }
.sidebar_left .inpaint:after{ background-image: url('images/icons/inpaint.svg'); }
.sidebar_left .text:after{ background-image: url('images/icons/text.svg'); background-size: 16px auto; }
.sidebar_left .gradient:after{ background-image: url('images/icons/gradient.png'); background-size: 18px 12px; filter: none; }
.sidebar_left .clone:after{ background-image: url('images/icons/clone.svg'); }
.sidebar_left .crop:after{ background-image: url('images/icons/crop.svg'); }
.sidebar_left .blur:after{ background-image: url('images/icons/blur.svg'); }
.sidebar_left .sharpen:after{ background-image: url('images/icons/sharpen.svg'); }
.sidebar_left .desaturate:after{ background-image: url('images/icons/desaturate.svg'); }
.sidebar_left .bulge_pinch:after{ background-image: url('images/icons/bulge_pinch.svg'); }
.sidebar_left .animation:after{ background-image: url('images/icons/animation.svg'); }

@media screen and (max-width:550px){
        left: -110px;

I suspect I need to create several CSS classes from the singular class that exists now, but I have no idea how to dd this (rookie!). Any amendments or different approaches would be very welcome.


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