is it better to implement child theme
Helix does not have this option. You can only create a copy of the template, not a child template. However, if you do not need to make global changes to index.php, you should not resort to this option, as your copy will not receive updates.
Simply create a custom.css file and write your code there, overriding the template styles.
it does. i don't know why and how but it does :-)
Going back to this, it could have happened for only two reasons:
- Evil Voodoo witchcraft.
- A syntax error on your part. Check all your CSS and make sure there are no mistakes, missing brackets, or similar issues.
In the case of CSS, restoring a backup is unnecessary. If something went wrong due to your CSS, simply delete it.