Update dark mode styles, fix black box on stories. Closes #2982

resources/assets/sass/appdark.scss

@@ -46,6 +46,10 @@
 	background: #000 !important;
 }
 
+.story-viewer-component-card {
+	background: transparent !important;
+}
+
 .autocomplete-result-list {
 	z-index: 99999;
 }