dark mode news improvs

Author: shravanngoswamii

theming/theme-dark.scss

@@ -242,6 +242,10 @@ a {
     background-color: $background-nav !important;
 }
 
+.quarto-post {
+    border-bottom: 1px solid #383838 !important;
+}
+
 code {
     background-color: $code-block-bg !important;
     color: $li-color !important;