Remove redundant blank line in CSS file

Eliminated an unnecessary blank line for cleaner and more consistent formatting. This improves the readability and maintains coding style standards.

src/browser/themes/shared/preferences/zen-preferences.css

@@ -576,7 +576,6 @@ groupbox h2 {
   cursor: pointer;
 }
 
-
 .zenThemeMarketplaceItemPreferenceDialog {
   display: flex;
   flex-direction: column;