i actually override the style.css in my interfece-child theme folder, and i set this rule at the top of my style.css (child) @import url(“../interface/style.css”);
overriding responsive.css is not as much easy as overriding style.css. So you need to first unhook the functions and then customize the code. We have replied many times how to unhook functions. You can simply search how to unhook functions. Other simple way is that can simply add your responsive.css code inside custom css. That would be great and no need to make child theme too.
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