[css-values-4] Align the ID with the nearby sections.

Author: tabatkins

css-values-4/Overview.bs

@@ -3061,7 +3061,7 @@ Argument Ranges</h4>
 	</div>
 
 
-<h3 id='calc-signs'>
+<h3 id='sign-funcs'>
 Sign-Related Functions: ''abs()'', ''sign()''</h3>
 
 	The sign-related functions--