Reduce duplication in .less files

[keforbes]

I noticed there were hardcoded colors in some .less files that were already defined in common.less so this is just some cleanup to use the variable from common.less instead. The only visual change I made was to the detail color in the menu and autocompletion. I think the detail text was too dim so I got rid of the alpha value but kept the color the same.

[keforbes]

Ok, one more visual change. In the menu, make the mouse hover color slightly dimmer than the selected item color so you can tell the difference.

[bryphe]

Thank you for cleaning this up! The changes you made to the detail text and hover color look great - it's a subtle but significant improvement in the completion / popup menu.