How to change font in widgets bar?

go to your appearance section and check your stylesheet for the sidebar and/or widget class attributes and find the one/s that are referencing the font styles. It’s hard to specifically direct you since theme files and stylesheets can be so varied, but that should get you in the ballpark, and you can hunt around changing variables, saving, refreshing (and undoing!) til you find which one is dictating the widget style you’re after.

Additionally, just in case it’s not a sidebar widget issue, check whatever the widget/plugin may be – this time go to plugins/editor and find the plugin in the drop down, find the related .css file and then see above.

That is a good idea. Thank you.