JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrapper">
    <div>1</div>
    <div>2</div>
    <div>3</div>
</div>

CSS

.wrapper {
    display: flex;
}
.wrapper > div {
    flex: 1 100%;
    height: 100vh;
    background: #999;
}
.wrapper > div:nth-child(2) {
    flex: 1 0 300px;
    background: #900;
}