[Gtk-3.22] Button-Redesign

[khurshid-alam]

So far we have been using our $theme_bg_color as button-background-color, which makes hover and focus state not recognizable (Issue #370 ). We tried increasing shadows and all. But that didn't work well and also it broke the theme design as Numix first and foremost is a flat theme. For action-buttons (suggested and destructive) we also need a separate mixing style rather than using same $bg color relative to lightness. Hover on active state in GtkListbox doesn't work either (button-hover-listbox]. Inline-toolbar and linked toolbar buttons seems to be broken as well. To address all those issues I am proposing following fixes. These changes are small and not so radical in-terms of design but that in terms of color.

Button-Fixes	Related-Issues	Status	Commit
1. Use darker $bg_color and lighter color for focus/hover state 2. Seperate light/dark button in terms of lightness 3. Fix background color inline-toolbar	#370		9e4844a7
Use new mixing for action-buttons	#370	.
Use new mixing for inline-toolbar buttons
Fix inline-toolbar-linked button
Fix focus/hover in active state under GtkListBox
Simplify sass rules for button mixing. Example: @mixin button($t, $actionb_bg, $actionb_fg) { // where $t: button_type (normal, suggested, headerbar, listbox etc) //$actionb_bg, $actionb_fg: action button bg/fg colors }