style(dashboard): refine background colors and remove backdrop filters for improved aesthetics

Entire-Checkpoint: 84693b066142

libs/workspace/dashboard/ui/src/lib/widgets/dashboard-activity-items.component.scss

@@ -222,8 +222,7 @@
     right: 4px;
     width: 24px;
     height: 24px;
-    background: color-mix(in srgb, var(--mat-sys-surface-container-highest) 90%, transparent);
-    backdrop-filter: blur(4px);
+    background: color-mix(in srgb, var(--mat-sys-surface-container-highest) 96%, transparent);
     opacity: 0;
 
     mat-icon {

libs/workspace/dashboard/ui/src/lib/widgets/dashboard-widget-shell.component.scss

@@ -24,9 +24,7 @@
     justify-content: space-between;
     gap: 12px;
     padding: 14px 16px 10px;
-    position: sticky;
-    top: 0;
-    z-index: 2;
+    flex-shrink: 0;
     background: var(--app-widget-header-bg, var(--mat-sys-surface-container-high));
     border-bottom: 1px solid var(--app-widget-header-border, rgba(255, 255, 255, 0.05));
 }