JSFiddle - React, Tailwind, and code Playground

HTML

<body>
        <div id="UpperLeftScanningIndicator"></div>
        <div id="UpperRightScanningIndicator"></div>
        <div id="Content">Here is some content.<br /><br /><br /><br />Here is some more.</div>
        <div id="LowerLeftScanningIndicator"></div>
        <div id="LowerRightScanningIndicator"></div>
    </body>

CSS

#Content {
    border: solid 1px black;
    width:90%;
    margin-left:auto;
    margin-right:auto;
}

#UpperLeftScanningIndicator {
    height: 20px;
    width: 20px;
    background-color: black;
    float: left;
}

#UpperRightScanningIndicator {
    height: 20px;
    width: 20px;
    background-color: black;
    float: right;
}

#LowerLeftScanningIndicator {
    height: 20px;
    width: 20px;
    background-color: black;
    float: left;
    position:absolute;
    bottom:20px;
}

#LowerRightScanningIndicator {
    height: 20px;
    width: 20px;
    background-color: black;
    float: right;
    position:absolute;
    bottom:20px;
    right:500px;
}