JSFiddle - React, Tailwind, and code Playground

HTML

<div class="parent">
<div class='content'>
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    <br />adfafhaskldjs sgdafadkfjas
    <br />saodfhdpaofa]sdoas [fdf asfasfjasfdkasfad;sdlafa dfasds dad gad
</div>
<div class='sidebar'>
    daobf haohf asod agsdjfa
    <br />sidja ofhad
    <br />sojgh fadpfjas
</div>
</div>

CSS

.parent
{
 position: relative;
}
.content {
    background-color: lightblue;
    margin-right: 120px;
}
.sidebar {
    position: absolute;
    top: 0px;
    right: 0px;
    width: 120px;
    background-color: lightgreen;
}
/* Responsive bit*/
@media only screen and (max-width: 320px) {
.content {
    background-color: orange;
    margin-right: 0px;
}
.sidebar {
    background-color: red;
    position: relative;
    width: 100%;
}
}