[css-variables] Remove extraneous explanator text about fallbacks and default values.

Author: tabatkins

css-variables/Overview.html

@@ -559,18 +559,8 @@ <h2 id="using-variables" data-level="3"><span class="secno">3 </span>
 		rather than the initial value.
 	</p></div>
 
-<p>	In some cases,
-	it can be useful to provide a "default" value for a variable
-	in case the variable isn't defined or is invalid.
 
-</p><p>	For example, if a site uses variables to provide "hooks" for customization,
-	expecting the variables to be defined in a separate custom stylesheet,
-	the main stylesheet can use default values for its variable
-	so that the theming stylesheet can just override the variables it cares about,
-	rather than being forced to provide values for all of them.
-
-
-</p><h3 id="invalid-variables" data-level="3.1"><span class="secno">3.1 </span>
+<h3 id="invalid-variables" data-level="3.1"><span class="secno">3.1 </span>
 Invalid Variables</h3>
 
 <p>	When a <a data-autolink="link" href="#custom-property">custom property</a> has its initial value,

css-variables/Overview.src.html

@@ -516,16 +516,6 @@ <h2 id='using-variables'>
 		rather than the initial value.
 	</div>
 
-	In some cases,
-	it can be useful to provide a "default" value for a variable
-	in case the variable isn't defined or is invalid.
-
-	For example, if a site uses variables to provide "hooks" for customization,
-	expecting the variables to be defined in a separate custom stylesheet,
-	the main stylesheet can use default values for its variable
-	so that the theming stylesheet can just override the variables it cares about,
-	rather than being forced to provide values for all of them.
-
 
 <h3 id='invalid-variables'>
 Invalid Variables</h3>