JSFiddle - React, Tailwind, and code Playground

HTML

<div id="simulated-html">
    <div id="footer">
        <span>
            Some footer text.
        </span>
    </div>
    <div id="simulated-body">
        

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CSS

* { margin:0; padding:0; }

html {
    font: 12px/1.5em Georgia;
}
p { padding: 5px; }

html, body {
    height: 100%;
    overflow: hidden; /* hide scrollbars, we create our own */
}

#simulated-html {
    background: orange;
    overflow-x: scroll; /* force horizontal scrollbars (optional) */
    overflow-y: hidden; /* hide. we use the #simulated-body for it. */
    position: relative; /* to align #footer on #simulated-html */
    height: 100%;
}

#simulated-body {
    overflow-y: scroll; /* force vertical scrollbars (optional) */
    overflow-x: hidden; /* hide. we use the #simulated-html for it. */
    height: 100%;
    background: #eee;
    
    /* use as a container */
    width: 450px;
    margin: 0 auto;
}

#footer {
    position: absolute;
    bottom: 0px; /* vertical align it to #simulated-html */
    width: 100%;
    background: red;
    z-index: 99; /* always show footer */
    color: white;
}
#footer span {
    width: 450px;
    margin: 0 auto;
    background: green;
    display: block;
}