JSFiddle - React, Tailwind, and code Playground

HTML

<div class="outer-container">
            <div class="button"></div>
            <div class="box">content here is variable</div>
    </div>

CSS

.outer-container {
    float: right;
}

.button {
    float: right;
    height: 35px;
    width: 35px;
    background-color: red;
}

.box {
    float: none;
    overflow: hidden;
    height: 35px;
    background-color: green;
}