[css-backgrounds] Add cross-reference to Corner Shaping from 'background-clip'

--HG--
extra : rebase_source : ea19c53c0ac4a23117280312282e1601282a976e

Author: fantasai

css-backgrounds/Overview.html

@@ -1421,6 +1421,11 @@ <h3 id=the-background-clip><span class=secno>3.7. </span>Painting Area: the
    border, if any. See “Elaborate description of Stacking Contexts” in <a
    href="#ref-CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>.
 
+  <p>See the section on <a href="#corner-shaping">Corner Shaping</a> for how
+   ‘<a href="#border-radius"><code
+   class=property>border-radius</code></a>’ affects the shape of the <a
+   href="#background-painting-area"><i>background painting area</i></a>.
+
   <p>See the section <a href="#layering">“Layering multiple background
    images”</a> for how ‘<a href="#background-clip"><code
    class=css>background-clip</code></a>’ interacts with other

css-backgrounds/Overview.src.html

@@ -913,6 +913,9 @@ <h3 id="the-background-clip">Painting Area: the 'background-clip' property</h3>
 the border, if any. See “Elaborate description of Stacking Contexts” in
 [[!CSS21]].
 
+<p>See the section on <a href="#corner-shaping">Corner Shaping</a>
+for how 'border-radius' affects the shape of the <i>background painting area</i>.
+
 <p>See the section <a href="#layering">“Layering multiple background
 images”</a> for how ''background-clip'' interacts with other
 comma-separated background properties to form each background image