1. how to converse em to px and vice versa ? 2. How to create a background
measured in em ?
The straight answer to both questions is "No". Assuming you indeed need this for web output, you have some serious reading up to do. Backgrounds can only be defined in percentages or absolute pixel values. The "em" measurement applies to any dynamically rendered page element that is able to inherit measurements – tables, text, divs, form controls and a few others, but not pixel images. However, even though it is used widespread, it is considered "bad style" as the output will look drastically different in every browser and severely may impair usability and accessibility (e.g. some elements could be rendered off-screen or become so small, they can’t be clicked). Therefore any sizes should be entered in pixels, points or percentages, or, where it applies, in the old-style fixed size increments (small, big, +1, +2,-1,-2 and so on).
Mylenium
