How to add two buttons on one line?

Sorry, I don’t understand. When I look at your site in Firefox, the buttons are on the horizontal line. Now, the page itself has some coding issues. Different browsers may process the errors differently, resulting in a different visual look. Whenever you see red coding in the page source view of Firefox, that’s an indication there was a problem the browser tried to fix.

Make sure you have all the appropriate closing tags: </p>, </div>, </a>, etc. You can also try running your html through this free, online utility: https://infohound.net/tidy/