Drawscript is an extension for Illustrator (a tool from Adobe® Creative Cloud) It generates graphics code from vector shapes in realtime. Obj-C C++ JavaScript Processing ActionScript 3 JSON Raw Bezier Points
A background image that fits the entire web page can be more challenging. I’ve learned that a simple graphic with a strong diagonal feel, sized to fit 100% of the page’s height and width, can be a fun and effective background graphic that seems to be a custom fit to the web page size