How can I stop Discourse from altering my Forum's design?

I’ve only modified the CSS of the site, as I’m not a developer and don’t know how to do anything else.

The theme I’m using for my forum is the Zeronoise theme that I found here on your website.

Thanks for your reply! However, it is not yet helping me understand what I’m doing wrong. If you can let me know what I’m doing wrong, then I can stop doing it. All the themes and theme-components that I install are from you guys. The CSS is the only thing I’m changing in those themes.

Is the way I’m loading the themes wrong? Please help me know what I’m missing because I really want to fix it so I don’t have to deal with random changes on my site’s design every few weeks.