TPAC: Improve style.css to reduce warnings

TPAC: Improve style.css to reduce warnings

* Improve specificity: use background-image (for gradients) or
  background-color (for color) instead of just background, because we
  are only specifying the image or color, and not the rest of the
  background properties.
* Declare the background-color first, followed by the background-images;
  these will only override if recognized by the browser.
* Declare the standard (unprefixed) CSS linear-gradient last to prevent
  prefixed browser quirk versions from overriding the standardized form.
* Remove the -moz- prefix from -moz-border-radius as that has not been
  supported by Gecko since Firefox 13.0; just plain border-radius now.
* Fix bad selector ##rdetail_extras_expand (only one #, please).

Signed-off-by: Dan Scott <dan@coffeecode.net>