User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_3) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/12.0.3 Safari/605.1.15

Steps to reproduce:

Add a display flex (or inline-flex) to a button that have padding and inspect it whit Firefox developers edition.

<style>
div, button{
padding:10px;
border:1px solid black;
display:inline-flex;
background:lime;
font-family:arial;
font-size:15px;
cursor:pointer;
}
</style>

<div>DIV</div>
<button>BUTTON</button>

Actual results:

Highlight fails to position elements ruler border because doesn't calculate padding.

Expected results:

highlight calculating padding as a DIV

Tested on Mozilla/5.0 (X11; Linux x86_64; rv:90.0) Gecko/20100101 Firefox/90.0
Issue appears resolved, but this was not tested on the same platform