feat: Add less opacity to the glance background, b=no-bug, c=common, glance

src/zen/common/styles/zen-panel-ui.css

@@ -51,7 +51,6 @@ panel[type='arrow']:not(#feature-callout) {
   }
 
   @media (-moz-platform: macos) {
-    border: 0px transparent !important;
     appearance: auto !important;
     -moz-default-appearance: menupopup;
     /* We set the default background here, rather than on ::part(content),

src/zen/glance/ZenGlanceManager.mjs

@@ -328,7 +328,7 @@
         parentSidebarContainer,
         {
           scale: [1, 0.98],
-          opacity: [1, 0.6],
+          opacity: [1, 0.5],
         },
         {
           duration: 0.3,
@@ -836,7 +836,7 @@
           browserSidebarContainer,
           {
             scale: [0.98, 1],
-            opacity: [0.6, 1],
+            opacity: [0.5, 1],
           },
           {
             duration: 0.3,