chore: add css variable for preferences background color [skip e2e]

packages/web/src/components/assets/com.standardnotes.theme-proton/index.css

@@ -40,6 +40,7 @@
   --sn-stylekit-accessory-tint-color-3: var(--warning);
   --sn-stylekit-accessory-tint-color-5: var(--success);
 
+  --preferences-background-color: var(--background-strong);
   --preferences-navigation-selected-background-color: var(--background-norm);
 }
 

packages/web/src/javascripts/Components/Preferences/PreferencesCanvas.tsx

@@ -9,7 +9,10 @@ import { FOCUSABLE_BUT_NOT_TABBABLE } from '@/Constants/Constants'
 const PreferencesCanvas: FunctionComponent<PreferencesProps & { menu: PreferencesSessionController }> = (props) => (
   <div className="flex min-h-0 flex-grow flex-col md:flex-row md:justify-between">
     <PreferencesMenuView menu={props.menu} />
-    <div className="min-h-0 flex-grow overflow-auto bg-contrast" tabIndex={FOCUSABLE_BUT_NOT_TABBABLE}>
+    <div
+      className="min-h-0 flex-grow overflow-auto bg-[--preferences-background-color]"
+      tabIndex={FOCUSABLE_BUT_NOT_TABBABLE}
+    >
       <PaneSelector {...props} />
     </div>
   </div>

packages/web/src/javascripts/Components/Preferences/PreferencesMenuView.tsx

@@ -24,7 +24,7 @@ const PreferencesMenuView: FunctionComponent<Props> = ({ menu }) => {
   )
 
   return (
-    <div className="border-b border-border bg-default px-5 py-2 md:border-0 md:bg-contrast md:px-0 md:py-0">
+    <div className="border-b border-border bg-default px-5 py-2 md:border-0 md:bg-[--preferences-background-color] md:px-0 md:py-0">
       <div className="hidden min-w-55 flex-col overflow-y-auto px-3 py-6 md:flex">
         {menuItems.map((pref) => (
           <PreferencesMenuItem

packages/web/src/stylesheets/_theme.scss

@@ -36,6 +36,7 @@
 
   --preferences-navigation-icon-color: var(--sn-stylekit-neutral-color);
   --preferences-navigation-selected-background-color: var(--sn-stylekit-info-backdrop-color);
+  --preferences-background-color: var(--sn-stylekit-contrast-background-color);
 
   --dropdown-menu-radio-button-inactive-color: var(--sn-stylekit-passive-color-1);