Can we make or download a custom dashboard or page for WF?

You can create layout templates to assign to users to dictate what they see from their main menu, top nav, object fields, etc. 

With the new Home, users can customize their own Home widgets (for a set of available widgets), and color of header area.

In Setup you can add a company logo and a couple branding-related things, but there isn’t a way to my knowledge that you can change any styling in code/HTML on the back end to change WF styling or layouts beyond this.