JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
    <div class="main-area">main content</div>
    <div class="sidebar">sidebar</div>
</div>

CSS

.container {
    position: relative;
}

.sidebar {
    position: absolute;
    top: 0;
    right: 0;
    width: 250px;
}
.main-area {
    background: red;
    margin-right: 250px;
}