Fix typo from 0effca0b2cc1e55ed3b12ea6a92a73a30698421c

BUG=411083
R=dbeam@chromium.org, stevenjb@chromium.org

Review URL: https://codereview.chromium.org/544273002

Cr-Commit-Position: refs/heads/master@{#293578}

ui/webui/resources/css/widgets.css

@@ -68,7 +68,7 @@ input[type='checkbox'] {
 <if expr="chromeos">
   bottom: 1px;
 </if>
-< expr="not chromeos">
+<if expr="not chromeos">
   bottom: 2px;
 </if>
   height: 13px;