[PM-3334] Update desktop dark theme to match browser (#5890)

* Update variables.scss

* update toast text color to have better WCAG contrast

* added toastcolor variables

* Update window.main.ts

* Tweaked styles

* darkened backgroundAlt2 and button background

* lightened button border

* lightened button backgroundColor

* Update window.main.ts

apps/desktop/src/main/window.main.ts

@@ -236,7 +236,7 @@ export class WindowMain {
       case "light":
         return "#ededed";
       case "dark":
-        return "#222222";
+        return "#15181e";
       case "nord":
         return "#3b4252";
     }