JSFiddle - React, Tailwind, and code Playground

HTML

<div class="outer">
    <div class="inner">
        some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text
        <img src="http://tinyurl.com/7pl9cw8" />
        <p>more text more text more text more text more text more text more text more text more text more text more text more text more text more text more text more text more text more text</p>
    </div>
</div>

CSS

.outer {
    margin: 40px;
    border: 2px solid black;
    padding: 10px;
    min-width: 404px;
}
.inner {
    border: 2px solid black;
    width: 400px;
}

JavaScript

function changeWidth() {
    var ele = document.getElementsByTagName("img");
    var width = (document.getElementsByTagName("div")[0].offsetWidth - 28) + "px";
    for(var i = 0; i < ele.length; i++) {
        ele[i].style.width = width;
    }
}
window.onload = window.onresize = changeWidth;