JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container" style="width: 100%;">
        <div class="left">
            Left div<br />
        </div>
        <div class="right">
            Right div<br />
            Right div<br />
            Right div<br />
            Right div<br />
        </div>
    </div>

CSS

.left {
    float: left;
    width: 250px;
    padding: 5px;
    border: 1px solid #ccc;
    
}

.right {
    width: auto;
    border: 1px solid #ccc;
    padding: 5px;
    margin-left: 261px;
    /* right margin-left = 250 + 5 +1 */
    /* if you want margin two div, you can write */
    /*  margin-left: calc(261px + 5px); */
}