JSFiddle - React, Tailwind, and code Playground

HTML

<div id="outer">
    <div id="inner1">
        Margin not coming from top (not absolute)
    </div>
    
    <div id="inner2">
        Div has absolue prop
    </div>
</div>

CSS

#outer {
    margin: 100px;
    background-color: green;
    height: 300px;
    width: 400px;
    border: 1px solid blue;
}

#inner1 {
    margin: 10px;
    background-color: red;
}

#inner2 {
    position: absolute;
    margin-top: 20%;
    background-color: blue;
    width: 360px;
}