[css=multicol-1] Updating image and example CSS, issue #3575

Author: rachelandrew

css-multicol-1/Overview.bs

@@ -999,8 +999,8 @@ Spanning columns</h2>
 <pre highlight="css">
 section {
 	border: 2px solid red;
-	margin-top: 3em;
-	padding-top: 2em;
+	margin-top: 65px;
+	padding-top: 20px;
 }
 
 h2 {