That means, you have customized the style in a wrong way.
Moreover, of course, you could customize the style, but in the proper way not in a wrong way.
If you customize the style in a wrong way, then it will raise issues like that you have already faced or others.
Please Note: If you are unable to customize the style in the proper way, then you need to hire someone else who is an expert in phpBB to customize the style for you based on your requirements.
Best Regards,
ThemeLooks Support Team