JSFiddle - React, Tailwind, and code Playground

HTML

<div class="width100">
    <div class="scroll">
        <div class="outer">
            <div class="border"></div>
            <div class="left"></div>
            <div class="right"></div>
        </div>
    </div>
</div>

CSS

.width {
    width:100%;
}
.scroll {
    overflow-x: scroll;
}
.outer {
    width: 960px;
    height: 55px;
    background-color: orange;
}
.border {
    width: 2px;
    height: 55px;
    margin-left:50%;
    position:absolute;
    background-color:black; // will be background-image with width: 960px;
}
.left {
    float: left;
    width: 400px; //varies
    height: 55px;
    position:relative;    
}
.right {
    width:560px; //varies
    float: left;
    height: 55px;
    background-color:green; // will be background-image with width: 960px;
}

JavaScript

$('.scroll')[0].scrollLeft = $('.left').width()