fixed typo error

fixed typo error

Author: singhabhinay

lib/web/css/docs/source/_popups.less

@@ -245,7 +245,7 @@
 //        <td>@popup-title-headings__level</td>
 //        <td class="vars_value">h3</td>
 //        <td class="vars_value">h1 | h2 | h3 | h4 | h5 | h6</td>
-//        <td>What heading style is applyed to the popup title</td>
+//        <td>What heading style is applied to the popup title</td>
 //      </tr>
 //      <tr>
 //        <th colspan="5" class="vars_section">Popup close button</th>