JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
    <div class="item">
        <div class="col w400p">
            lorem lorem
        </div>
        <div class="col">
            <p>right</p>
        </div>
    </div>
</div>

<div class="container">
    <div class="item-2"><!-- you also need a clearfix if left part is taller than the right one -->
        <div class="left w400p">
            lorem lorem
        </div>
        <div class="other">
            <p>right
                <br>
                <br>
                <br>
                <br>
                right
            </p>
        </div>
    </div>
</div>

CSS

.container {
    padding: 15px;
    border: 1px solid #000;
}
/* first example */
.item {
    display: table;
    width: 600px;
    table-layout: fixed;
    padding: 15px;
}
.col {
    display: table-cell;
    vertical-align: top;
    padding: 40px 20px;
    background-color: lightblue;
}
.col + .col,
.other {
    padding: 0;
    background-color: tomato;
}
/* second example */
.item-2 {
    width: 600px;
    padding: 15px;
}
.left {
    float: left;
    padding: 40px 20px;
    margin-right: 10px;
    background-color: lightgreen;
}
.other {
    overflow: hidden;
}

.w400p {
    width: 400px;
}