This of course is a wide field, and it should suffice to give a few hints here. Everything else is up to your imagination.
The HTML output of dbslide is CSS-aware. That is, it will use a cascading stylesheet dbslide.css if it is provided in the same directory as the HTML files. In fact, without such a stylesheet the HTML pages will look pretty much like the standard DocBook output, save a few minor changes. In order to manipulate the output, you can do two different things: edit dbslide.dsl and edit dbslide.css.
This is the DSSSL stylesheet that determines how the HTML code is generated by Jade or OpenJade. Edit this file to change:
the JavaScript/JScript code. This controls the keyboard and mouse navigation.
the name or type of the stylesheet for the browser display
The file is a "driver file" for Norman Walsh's modular DocBook stylesheets. The basic idea is that any definitions in this file override the default settings in the DocBook stylesheets. You can wade through the DocBook stylesheet files and look for interesting things to modify or extend.
This is the CSS stylesheet that determines how the HTML code is displayed by a CSS-aware web browser. Edit this file to change:
fonts
font sizes
colors
Before you set out to frantically change the sample stylesheet provided with the dbslide package, keep in mind that many fancy things that you could do with CSS will work only in one (or none) of the major browsers, or only on one platform. Unless you want to get the most fancy output possible by restricting yourself to one browser, it's best to keep things simple.