Changing unsemantic grid breakpoints

Hi Tom

I need to change the breakpoint at which the tablet classes kick in in the unsemantic grid stylesheet. I'm reluctant to do this in unsemantic-grid.css in the parent theme as my changes will be overridden next time there's a theme update.

Is it possible to create a second unsemantic-grid.css in my child theme folder which will override the one in the parent theme? Or a different solution? The only way I've found to fix this so far is by resetting some of the class values like this:

@media (min-width: 768px) and (max-width: 1215px) {
         .grid-25 {
		width: 50%;
	  }
}

to force the div to display at 50% even though the "grid-25" class is still being applied, which is just really inelegant and (ironically) totally unsemantic!

I'm aware this is more a general CSS question than a GeneratePress question but I'm tearing my hair out trying to find a solution so any help would be really welcome!

Thank you!
Caroline