On the right-hand, Theme Files, click on assets>css>main.css and this is what you should see:

After clicking on main.css, you should now see the main stylesheet.

Never make any changes to the parent stylesheet, at best, any changes you make will be lost if the theme is updated, at worst you could break your site.

Any changes you make should be done in Additional CSS or a Child Theme.

Thanks you for viewing this tutorial, if you found it helpful a like/comment would be much appreciated.