Improved: Alternative Dark theme (#4635)

* background colors

* border

* Update adark.css

* font-color

* empty feed color

* slider

* color input improved

* menu nav hover

* nav: highlight font color while hovering

* lighter color btn icon on hover

* btn-attention background color

* empty feed color

* delete .log CSS

* delete white background .icon when feed active

* article header+footer

* bigMarkAsRead button

* .content hr

* dropdown triangle color

* rename variables

* notification colors

* border colors

* last left colors

* reorder

* hover flux icons

* config dropdown menu mobile view shadow+border

* dropdown menu hover color

* close aside hover

* slider-shadow

* icon hover

* toggle aside

* improved contrast blue

* contrast border color hover

* kbd styled

* hover on form elements highlight font color

* font colors instead background color

* link in alert

* contrast attention font color

* fix stream last item border

* font color of author in stream

* lighter color for headlines in article

* nav: active menu entry in lighter font color

* Update adark.rtl.css

* fixes

* fix favicon hover

* fix