How to change the color of the burger-three-lines of the mobile menu toggle button in Olivero?

This works:

.mobile-nav-button__icon,
#site-header__inner > div > div.mobile-buttons > button > span.mobile-nav-button__icon:before,
#site-header__inner > div > div.mobile-buttons > button > span.mobile-nav-button__icon:after {
	border-top: 3px solid #fff;
}

What an awful way to make a burger button; there is a standard Unicode character for that (☰).

Please do not complain about the community-maintained and open-source software. Contribute → .

Cilefen? please define "complain" ; criticism is allowed and often required ; especially from someone who can't contribute on a specific matter (I am not a Drupal themer) ; I will edit the phrasing.

Criticize by contributing fixes please. There could well be good reasons the menu is implemented the way it is, or, it may be an inefficient solution. You won't get a lot of support here by calling the code "awful".

contributing fixes is not and should not be the only way to criticize open source software.

I have changed the phrasing of the sentence with that word.