JSFiddle - React, Tailwind, and code Playground

HTML

<div class="main">
    <div class="parent">
        <div class="child"></div>
        <div class="child"></div>
        <div class="child"></div>
    </div>
</div>

CSS

.main {
    width : 400px;
    height: 400px;
    border :1px solid black;
}
.parent {
    width: 100px;
    height: 400px;
    border-left: green 5px solid;
    z-index: 100;
}
.child {
    width : 100px;
    height: 100px;
    background: red;
    z-index: -1;
    margin-left: -5px;
    border: black 5px solid;
    position: relative;
}