If you decide to go ahead with direct edits anyway, use a file manager to create a copy with a new name and hang on to the original. That way, you can re-enable a functional version if something goes wrong.
Child Theme Recommendation
If you need to tweak more than your theme’s CSS, you might want to try making a child theme.
Direct Theme Edits Warning
You appear to be making direct edits to your theme in the WordPress dashboard. It is not recommended! Editing your theme directly could break your site and your changes may be lost in future updates.