"Allow people to use a predefined CSS design instead of writing your own."

Several of your historical responses have informed you that css is customisable, in terms of a single pre defined change see Display Settings -> 'Theme container'.

"And the website should allow people to post pictures if they want to."

People can link to an image should they wish, outside of home node images I see no benefit to the burden of hosting them here. It'd add more janitorial work.

"Have the ability to upload a zip file into each person's profile."

This creates more problem and janitorial headaches than it solves problems, github (along with their gists), gitlab (along with their snippets) and a multitude of other sites and services provide this. People already do this and just link to the information. It's a wheel that no one need reinvent here.