tweak <pre> text wrapping when displaying diff

backend/static/styles/diff.css

@@ -12,7 +12,8 @@
     border: 1px solid transparent;
     vertical-align: top;
     font: 1em monospace;
-    text-align: left;
+    text-align: left; }
+  #diff-ui pre {
     white-space: pre-wrap; }
 
 h1 {

backend/static/styles/diff.scss

@@ -16,9 +16,10 @@
         vertical-align: top;
         font: 1em monospace;
         text-align: left;
+    }
+    pre {
             white-space: pre-wrap;
     }
-
 }
 h1 {
 	display: inline;