JSFiddle - React, Tailwind, and code Playground

HTML

<p>Use box-sizing: border-box to create a border INSIDE a div without modifying  div width.</p>
<div id="test">border-box</div>
<p>Use outline to create a border OUTSIDE a div without modifying  div width.</p>
<div id="test2">outline</div>

CSS

#test, #test2 {
    width: 100px;
    height:100px;
    background-color:yellow;
}
#test {
    -webkit-box-sizing: border-box;
    -moz-box-sizing: border-box;
    box-sizing: border-box;
    border: 10px dashed blue;
}
#test2 {
    outline: 10px dashed red;
}