I don’t know if the normal variable linking way work for the variables in wix email’s html component but it said js is not supported but the variables are allowed?
Javascript isn’t supported in emails as it opens additional concerns related to security.
And yes - if you’re using triggered emails, the variables you use in the triggers can be used in the HTML template in the same way you would define the variables in the other email elements 
I found some problem. Is css restricted?
Like “positioning” and flexbox methods not work in html code.
Everything that is supported can be found here - Adding HTML to Your Email Template | Help Center | Wix.com - and you’re best to use inline styles
You can get pretty creative with it - for example, here’s an email I used to send to our team internally, where this whole image was HTML with inline styles and dynamic values 
