Is there a specification or a link or something?
Part of https://www.w3.org/TR/css-ui-4/ maybe?

MDN link: https://developer.mozilla.org/en-US/docs/Learn/Forms/Advanced_form_styling#selects_and_datalists

"The second, slightly more major issue is that you don't have control over the box that appears containing the options when you click on the box to open it. You'll notice that the options don't inherit the font set on the parent. You also can't consistently set things like spacing and colors. For example, Firefox will apply color and background-color when set on the elements, Chrome won't. Neither of them will apply any kind of spacing (e.g. padding). The same is also true of the autocomplete list that appears for the datalist." Seems to be based on browser renderer's decision rather than any specification. Setting color/background-color also does not work in Safari.

Is this related to the notes on label, as provided by MDN data?
https://caniuse.com/mdn-html_elements_option_label

(via mdn/browser-compat-data#373)

Is this related to the notes on label, as provided by MDN data? https://caniuse.com/mdn-html_elements_option_label

(via mdn/browser-compat-data#373)

I think so.