How to Create Popup in Wordpress Without Plugin?

Thanks for the information :)

Looks simple, and no added plugin is always a plus.

If I add the code by the Code Snippet plugin, will it work?

Not working.

Dont have a Theme editor..

no plugin but still reliying on a third-party tool. How come you are first search result on Google???

Best practice would be to use the Child Theme so the header.php file doesn`t get overwritten on subsequent updates.

I didn't get that popup after doing this i can see the code on top of website rather👎

Thanks for the clear information within a minute