updated colors in theme_default.css (effects the shading of alternating rows in the main top level category tables) to match the color scheme in the stix diagram icons

warning: the following do not have css styles yet because they don't have top level category tables (I will be adding these):
 - course of action
 - data marking
 - sighting
 - victim targeting
added some css tweaks to get styling more correct

swapped out a background color that was used for shading "expandables" with a very light gray border.  this allows the underlying background color to be displayed.