We don't have "highlighting" here. We have formatting, and formatting serves a semantic purpose:
- Italic text is for emphasis, like the HTML
- Bold text is for strong emphasis, like the HTML
Code formatting is for inline code snippets, like the HTML
You do want to make sure that you do not overuse emphasis, because when everything is emphatic, nothing is emphatic. There is no reason to set half of your post in bold. Not all of that text needs to be emphasized. If people want to know what you have to say, they'll read your answer. Use this sparingly.
Furthermore, there is a growing trend of people abusing inline code formatting as some kind of "highlighting" effect. That's not what it is for. The clue is in the name: code formatting. If it is not code or some identifier found in code, it does not belong between backticks. Period.
And yes, this type of abuse should be removed by editors, whether they are moderators or just regular users. It cleans up the site, making the post easier to read and less of an eyesore. You should be thanking them, this kind of abuse of formatting tends to attract downvotes and other negative attention.
As for specifics: I assume that you mean this answer, which was recently edited by BoltClock. Indeed, as I suspected, you had abused backticks for regular words that were not code. Please do not do this. Sibling is just a regular English word. It is descriptive of something found in code, but it is not itself an identifier used in CSS. Setting "header" in inline code formatting was acceptable there, though, because "header" is actually a symbol used in the code. BoltClock left that alone. And there was no reason to bold CSS. Everyone reading the question knows that it's about CSS. Leaving "tilde" bolded would have been fine; that's just a judgment call. But if you tend to overdo formatting, people tend to overdo when removing it.