Answer 1

Site can be fully functional with only html and css, if goal of site is to display some fixed information.

Javascript is used to react to user action, like button click, key pressed and others.( most site have hamburger menu for example, when user click it show nav element - for this you need to know javascript)

Js is also used to make layout dynamic, and reusable, to fetch data from API or database...

If you wanna site like e-commerce , social network, you also need backend language(here python can be used)

So if you wish full stuck website idea, then check this:
https://www.knowledgehut.com/blog/web-development/full-stack-development-projects

Answer 2

Please remove from tags, javascript and python, sololearn, if your question is not about them.

For html and css you can make design of any webpage. So go to internet, find some site and try to recreate it, you can also inspect element to see how they create site.

For some other projects, you can make:
1. landing website - website about some product, or movie...
2. Restaurant website
3. Your portfolio
4. Form - you can add functionality latter when you learn javascript or even some backend
5. Animation
6. Draw something with html and css only (you can watch tutorial if you stuck)
7. Tribute page - page about some person

try to use as much as possible html tags and css styles, so you can practice everything