Replacing global themed sass-vars to css-vars (#4322)

* generating css-vars
* convert all global / theme sass vars to css vars with available default theme colors
* added missing colors to dark lens theme

src/renderer/components/item-object-list/item-list-layout.scss

@@ -20,7 +20,7 @@
  */
 
 .ItemListLayout {
-  background: $contentColor;
+  background: var(--contentColor);
   height: 100%;
 
   > .header {

src/renderer/components/item-object-list/page-filters-list.scss

@@ -20,12 +20,12 @@
  */
 
 .PageFiltersList {
-  $bgc: $filterAreaBackground;
+  $bgc: var(--filterAreaBackground);
   $spacing: $padding * 1.5;
 
   position: relative;
   top: 1px;
-  border-top: 1px solid $borderFaintColor;
+  border-top: 1px solid var(--borderFaintColor);
   background: $bgc;
   padding: $spacing $padding * 2;
   font-size: $font-size-small;
@@ -36,7 +36,7 @@
   }
 
   &:not(:empty) {
-    border-bottom: 1px solid $borderFaintColor;
+    border-bottom: 1px solid var(--borderFaintColor);
   }
 
   > .header {