[css-color-4] clarify exported D50 & D65

Author: svgeesus

css-color-4/Overview.bs

@@ -292,13 +292,13 @@ Value Definitions</h3>
 		</thead>
 		<tbody>
 			<tr>
-				<td><dfn export>D50</dfn></td>
+				<td><dfn export lt="D50 whitepoint" local-lt="D50">D50</dfn></td>
 				<td>0.345700</td>
 				<td>0.358500</td>
 				<td>5003K</td>
 			</tr>
 			<tr>
-				<td><dfn export>D65</dfn></td>
+				<td><dfn export lt="D65 whitepoint" local-lt="D65">D65</dfn></td>
 				<td>0.312700</td>
 				<td>0.329000</td>
 				<td>6504K</td>