What do strikethrough lines in CSS code mean when viewed in Google Chorme?

Question

css

I study only HTML, CSS, along the way creating my own website. Another bunch of questions about WordPress, the server and other subtleties. But here I am peeping at other people's sites, according to the principle of which I want to do it, and there some properties, for example, are crossed out, while the rest are not.
In some places "font-size: 100%; " is crossed out, but below it is not.
And is there any manual for "View element code"?

Answer 1

The rule is overridden by a higher priority selector

Answer 2

it means that this css rule is overridden, read about css property prioritization and inheritance

Answer 3

The rule is overridden by a higher priority selector, or the rule is written with an error
, for example, dispay: none // heigt: 100%