I am new to wordpress development and I've read the documentation on how to do what I want to do but I can't find any decent answers.
I want to make a plugin that can show a popup window when someone goes to a certain page. the info in the popup will be customizable based on what the admin wants to show but I cannot figure out how to add css and js to the page the visitor is currently on. Basically injecting html and css into the body. I'm a junior developer and I've never worked with php or wordpress before (until a week ago when my boss asked me to make this wordpress plugin) but I know JS quite well.
any help or pointing in the right direction would be appreciated.