Frontpage: Fix rss link color, better selector

Also fixed Stylelint quotes issue introduced earlier.

Author: silverwind

github-dark.css

@@ -1599,7 +1599,7 @@
   .markdown-format h6 .octicon-link, .tabnav-tab.selected,
   .leaflet-control-attribution, .leaflet-control-attribution a,
   .integrations-breadcrumb-link, a.integrations-breadcrumb-link,
-  .ace_button {
+  .ace_button, .link-gray-dark, a.link-gray-dark {
     color: #e0e0e0 !important;
   }
   b, strong, .explain strong {
@@ -2180,13 +2180,13 @@
     background-repeat: no-repeat !important;
   }
   .network-tree[src$="t.png"] {
-    background-image: url('data:image/gif;base64,R0lGODlhFAAaAPABADMzMwAAACH5BAUAAAEALAAAAAAUABoAAAIkjI+pG8APY5O0uorfzRzt3n1g5pSTOTJiSq1s5L6ajMW0YgcFADs=') !important;
+    background-image: url("data:image/gif;base64,R0lGODlhFAAaAPABADMzMwAAACH5BAUAAAEALAAAAAAUABoAAAIkjI+pG8APY5O0uorfzRzt3n1g5pSTOTJiSq1s5L6ajMW0YgcFADs=") !important;
   }
   .network-tree[src$="i.png"] {
-    background-image: url('data:image/gif;base64,R0lGODlhFAAaAPABADMzMwAAACH5BAUAAAEALAAAAAAUABoAAAIhjI+pG8APY5O0uorfzRzt3n1gJo6WGaJcqUJsy7ywIgcFADs=') !important;
+    background-image: url("data:image/gif;base64,R0lGODlhFAAaAPABADMzMwAAACH5BAUAAAEALAAAAAAUABoAAAIhjI+pG8APY5O0uorfzRzt3n1gJo6WGaJcqUJsy7ywIgcFADs=") !important;
   }
   .network-tree[src$="l.png"] {
-    background-image: url('data:image/gif;base64,R0lGODlhFAAaAPABADMzMwAAACH5BAUAAAEALAAAAAAUABoAAAIejI+pG8APY5O0uorfzRzt3n1g5pSTOabqyrbuC68FADs=') !important;
+    background-image: url("data:image/gif;base64,R0lGODlhFAAaAPABADMzMwAAACH5BAUAAAEALAAAAAAUABoAAAIejI+pG8APY5O0uorfzRzt3n1g5pSTOabqyrbuC68FADs=") !important;
   }
   /* octotree icons */
   a.octotree_toggle:not(.octotree_loading) > span:after,
@@ -2303,7 +2303,7 @@
   }
   /* orange rss icon */
   .blog-aside .octicon-rss, .dashboard-feed-icon.octicon-rss,
-  .nav-rss a .octicon-rss, a.feed-icon, #dashboard .octicon-rss {
+  a .octicon-rss, a.feed-icon {
     color: #f93 !important;
   }
   .featured-label {