There are two ways to do this:
- You can copy the original LESS file from
vendor/magento/theme-frontend-blank/Magento_Catalog/web/css/source/_module.less to your custom theme. This can be used when you want to override a lot of stuff in that file.
- You can create a new file called
app/design/frontend/gog/gogparent/Magento_Catalog/web/css/source/_extend.less. In this file you can add all your custom styling, which comes on top of the default styling of
Magento_Catalog that's in the Blank theme.
Personally I'm more a fan of option 2, since that reduces the number of work you have when upgrading Magento, because if the styling of a module changes in the Blank theme, you don't have to copy the entire file. And I like to add an addition to option 2 as well. What I normally do is this:
Now I put all my customisations into these separate files, which gives me a much better overview of the changes per pagetype. You only need to create a folder
app/design/frontend/gog/gogparent/Magento_Catalog/web/css/source/extend and put all these separate less files in there.