MAGETWO-37920: Add documentation for Styles Library components

- CR changes

Author: Bogdan Plieshka

lib/web/css/docs/variables.html

@@ -6045,7 +6045,7 @@ <h3 id="cross-components-variables">Cross Components variables</h3>
         <th>@component__shadow-size__base</th>
         <td class="vars_value">5px</td>
         <td class="vars_value">constant</td>
-        <td>Shadow size, cross all components. Use to count overlay zones sizes</td>
+        <td>Shadow size across all components. Used to count overlay zones sizes</td>
       </tr>
       <tr>
         <th>@component__box-shadow__base</th>