JSFiddle - React, Tailwind, and code Playground

HTML

<div id="header">
    <div class="container">
        header
    </div>
</div>
<div id="content" class="container">
    <div class="inner">
        content
    </div>
</div>
<div id="sidebar">
    <div class="container">
        <div class="inner">
            sidebar
        </div>
    </div>
</div>

CSS

body {
    padding: 0px;
}
.container {
    margin: 0px auto;
    position: relative;
    width: 500px;
}

#header {
    left: 0px;
    position: fixed;
    top: 0px;
    width: 100%;
    z-index: 1000;
}
#header .container {
    background: blue;
    height: 100px;
}

#content {
    background: green;
    height: 1500px;
    margin-top: 100px;
}
#content .inner {
    margin-right: 200px;
}

#sidebar {
    left: 0px;
    position: fixed;
    top: 100px;
    width: 100%;
    z-index: 1000;
}
#sidebar .inner {
    background: red;
    height: 200px;
    position: absolute;
    right: 0px;
    top: 0px;
    width: 200px;
}