change(colors): added backgroundColorSupplementary color variable

- as defined in docusaurus our main bg color is white but we
  also have a supplementary bg color which is now set to F9F9F9
  as such we need to define this color as well
- use pure white for text color of themed content boxes

theme/themes/eea/extras/contentBox.less

@@ -49,10 +49,10 @@
   --bg-color: transparent;
   --border-color-secondary: #FFF;
   --text-color: #FFF;
-  --text-color-primary: @grey-1;
-  --text-color-secondary: @grey-1;
-  --text-color-tertiary: @grey-1;
-  --text-color-hover: @grey-1;
+  --text-color-primary: #FFF;
+  --text-color-secondary: #FFF;
+  --text-color-tertiary: #FFF;
+  --text-color-hover: @backgroundColorSupplementary;
 }
 // inherit link
 .content-box[class*="ary"] a:not(.ui, .item) {

theme/themes/eea/globals/site.variables

@@ -191,8 +191,10 @@
 @borderColorSecondaryCSSVar: var(--border-color-secondary, @secondaryColor);
 @borderColorTertiaryCSSVar: var(--border-color-tertiary, @tertiaryColor);
 @contentAreaColor    : @tertiaryColor;
-@backgroundColor: @grey-1;
+@backgroundColor: @grey-0;
 @backgroundColorCSSVar: var(--bg-color, @backgroundColor);
+@backgroundColorSupplementary: @grey-1;
+@backgroundColorSupplementaryCSSVar: var(--bg-color-supplementary, @backgroundColorSupplementary);
 
 /*-------------------
       Paragraph