[navSide] inconsistent css vars naming and usage

[BertrandPodevin]

NavSide CSS vars names and usage for the colors is inconsistent.

One example : the background-color of the components (navide and navside alert) are sometimes defined with a --xxxx-color, sometimes with a --xxxx-bg, sometimes with a --xxxx-bg-color and in one occurence with a --xxxx-text.

There are css vars for some states (hover, selected).. but not for active wich lead to other inconsistent usage of vars.

My opinion :

• Background-color should always be defined with a css vars --xxxx-background-color
• Color should always de defined with a css vars --xxxx-color.
• States (hover, active, selected) should never inverse the use of a background-color and a color css vars. (color: --xxxx-background-color, background-color: --xxxx-color) but should instead define specific css vars. (ex --xx-active-background-color).