Fix Dark load (#2987)

#fix https://github.com/FreshRSS/FreshRSS/issues/2986 😈😛

p/themes/Dark/dark.css

@@ -771,6 +771,7 @@ a.btn {
 
 /*=== Feed articles */
 .flux {
+	background: #1c1c1c;
 	border-left: 2px solid #2f2f2f;
 }
 

p/themes/Dark/dark.rtl.css

@@ -771,6 +771,7 @@ a.btn {
 
 /*=== Feed articles */
 .flux {
+	background: #1c1c1c;
 	border-right: 2px solid #2f2f2f;
 }