Usually upon searching a word in the search tab, if the word is in the page you’re on it will be highlighted yellow, like this:
However today I was doing a lot of formatting and noticed that if the text is written inside
<details><summary><kbd><b>
Then it disappears when searched.
For example:
Then when you search “staff”:
Try it yourself!
Now search “bug”! It will disappear.
That is really cool!
kbd * * {
display: none;
}
You’ve got kbd → strong → span class="search-result"
please translate into English 
CSS Rule what is happening, in short search is trying to put a highlight on your found word and the extra tag it places on your word causes kbd * * to run its display none rule.
Testing this again without the detail summary
Oo, it doesn’t have to be in details summary, just kbd and b.
kbd with your specific text in 1 nested tag. b, i, u, s, whatever.
Thanks @FHTzoob for reporting that issue. I just pushed a fix for the CSS 
https://github.com/discourse/discourse/commit/2a7af5e718583efef800fcfe19640e85b3815407