Mark OPs in MD theme with contrast background and border

boards/static/css/md/base_page.css

@@ -589,6 +589,9 ul {
 }
 
 .post[data-opening=True] > .post-info {
-    font-weight: bold;
+    background: black;
+    display: table;
+    padding: 4px;
+    border: white 1px solid;
 }