Adding anchor links to a page in Craft theme that accounts for header

[HRAF]

How to add some anchor links into a page in a Craft theme website? It's fine to create the anchors but then due to the header height the links take you too far down the page. 

This advice online (https://community.shopify.com/c/shopify-design/can-i-link-a-button-to-a-specific-section-on-a-page/m...) suggests adding this into the CSS: a.anchor{display: block; position: relative; top: -250px; visibility: hidden;} but when I added the code into the Custom CSS it wouldn't save / said online store editor session can't be published. 

Trying to create a 'contents' at top of an instructions page with links down to the different sections. 

[qasim-devloper]

May I know do you follow the all steps that shared in the link?
If yes then could you please tell me which issue you are facing whilie Saving. If possible a ScreenShot can be helpful.
Thanks

[HRAF]

Thanks for replying - above is a screenshot of where I was trying to add the custom CSS in the customize theme section.

[qasim-devloper]

Oh,
I think in your store there ie no class name by .anchor

[qasim-devloper]

Could you p/m me so that I provide you solution code.

[HRAF]

Sorry I'm not sure how to p/m you on here...

[qasim-devloper]

You can see my w*tp here.

[HRAF]

Sorry I'm not comfortable sharing access to our site over what's app. I'm sure it's all OK but I'm not permitted to give access to someone else externally. Thank you for trying to help