It seems you had created child theme on your own. And might be there is something wrong on child theme or cache is not letting browser to update you css.
So we request you to clear cache issue and also you can use child theme that comes on theme bundle itself[ “bundled file that comes when downloading from styledthemes.com”]. As that css works fine here and other site too
So if still these doesn’t help you . let us to fix your issue providing wp login details.