Hi
I have checked your site and both the issue you mentioned above. But Unfortunately, I am not able to see it. The registration form page is already centered and everything looks good.
If the issue still persists from your side, can you please share the URL link of the page where I can confirm your issue and fix it.
And for rounded corners of courses on the homepage is already rounded, check the screenshot below:
http://prntscr.com/olz9e5