fix wiki falsh message

lms/static/sass/course/wiki/_wiki.scss

@@ -885,8 +885,7 @@ section.wiki {
 
   .alert {
     position: relative;
-    top: -15px;
-    margin-bottom: 24px;
+    margin: 24px 40px;
     padding: 8px 12px;
     border: 1px solid #EBE8BF;
     border-radius: 3px;
@@ -903,6 +902,10 @@ section.wiki {
     }
   }
 
+  .main-article .alert {
+    margin: 0 0 24px;
+  }
+
   .missing {
     max-width: 400px;
     margin: lh(2) auto;