Use fontawesome icon for the HTML details element

As discussed in the Mattermost channel, I replaced the default triangle with Fontawesome icons.

_sass/common/_general.scss

@@ -95,3 +95,25 @@ h2 {
         width:          100%;
     }
 }
+
+// Replace the HTML details triangle with Fontawesome icons
+summary {
+    list-style: none;
+
+    &::-webkit-details-marker {
+        display: none;
+    }
+}
+details {
+    summary::before {
+        content: "\f138"; // fas fa-chevron-circle-right
+        font-family: "Font Awesome 5 Free";
+        font-weight: 900;
+
+        margin-right: 0.25rem;
+    }
+
+    &[open] summary::before {
+        content: "\f13a"; // fas fa-chevron-circle-down
+    }
+}