Add selectors for urlbar-background as class

chrome/compact_urlbar_megabar.css

@@ -17,6 +17,7 @@ See the above repository for updates as well as full license text. */
 .urlbarView-row-inner{
   padding-inline-start: 4px !important;
 }
+:where(#urlbar) > .urlbar-background,
 #urlbar-background{
   animation: none !important;
 }

chrome/rounded_menupopups.css

@@ -16,6 +16,7 @@ menupopup,
 
 /* The rounding is also applied to searchbar and urlbar to look consistent */
 searchbar#searchbar,
+:where(#urlbar) > .urlbar-background,
 #urlbar-background{
   border-radius: var(--uc-menupopup-border-radius) !important
 }

chrome/selected_tab_as_urlbar.css

@@ -28,6 +28,7 @@ See the above repository for updates as well as full license text. */
 }
 .urlbar-input-container > :not(.urlbar-input-box){ opacity: 0 }
 
+:where(#urlbar) > .urlbar-background,
 #urlbar-background{
   background: transparent !important;
   border: none !important;

chrome/show_urlbar_button.css

@@ -21,11 +21,11 @@ See the above repository for updates as well as full license text. */
   z-index: 1;
   inset-inline: 15vw !important;
 }
-:root:not([customizing]) #urlbar:not(:focus-within) > #urlbar-background{
+:root:not([customizing]) #urlbar:not(:focus-within) > :is(#urlbar-background,.urlbar-background){
   background: transparent !important;
   border-color: transparent !important;
 }
-:root:not([customizing]) #urlbar:not(:focus-within):hover > #urlbar-background{
+:root:not([customizing]) #urlbar:not(:focus-within):hover > :is(#urlbar-background,.urlbar-background){
   background: var(--toolbarbutton-hover-background) !important;
 }
 #urlbar:not(:focus-within) #page-action-buttons,

chrome/urlbar_container_color_border.css

@@ -33,7 +33,7 @@ See the above repository for updates as well as full license text. */
   position: static !important;
   padding: calc(2px + var(--urlbar-margin-inline,5px)) !important;
 }
-#urlbar[open] > #urlbar-background{ z-index: -1 !important; }
+#urlbar[open] > :is(#urlbar-background,.urlbar-background){ z-index: -1 !important; }
 
 /* OPTIONAL FEATURES */