Bootstrap uses background images to convey meaning on some controls. This is considered a failure when testing for accessibility for people with disabilities. about bootstrap

[patrickhlauke]

Background images that convey meaning are considered a failure when testing for accessibility for individuals with disabilities

If there is no other (programmatic, or in text) way in which the meaning is conveyed, yes. However, if the controls already convey their purpose through the actual element used, or explicitly via role="…", then they pass WCAG.

not relying on background colour/images is more a best practice to make things more likely to work for forced colour/high contrast modes, or for users that run custom stylesheets. but it goes beyond WCAG compliance.

[patrickhlauke]

Closing as the general idea (for forced colour/WHCM) is captured here already #35941