Step 1: After opening the FTP/Cpanel go to the following path(/templates/cloudx/css/)
Step 2: In next, you will see this file (cloudx_overrides.css_new) you have to remove the_new so that the file will be cloudx_overrides.css
Step 3: After renaming your file name it should be looked like this (cloudx_overrides.css) as mentioned in below screenshot. So that it will automatically included on theme and you can override any existing rule of css or add your own. This file will never be replaced in upcoming update of theme.