[css-background-4] Fix the most serious of the bikeshed linking warnings.

Author: dbaron

css-backgrounds-4/Overview.bs

@@ -128,7 +128,7 @@ Background Positioning Longhands: the 'background-position-x', 'background-posit
 	</pre>
 
 	This property specifies the background position's inline-axis component.
-	An omitted origin keyword is assumed to be ''start''.
+	An omitted origin keyword is assumed to be ''background-position-inline/start''.
 
 	<pre class='propdef'>
 		Name: background-position-block
@@ -142,7 +142,7 @@ Background Positioning Longhands: the 'background-position-x', 'background-posit
 	</pre>
 
 	This property specifies the background position's block-axis component.
-	An omitted origin keyword is assumed to be ''start''.
+	An omitted origin keyword is assumed to be ''background-position-block/start''.
 
 <h2 id="corners">
 Corners</h2>

css-backgrounds-4/Overview.html

@@ -345,7 +345,7 @@ <h4 class="heading settled" data-level="2.1.1" id="background-position-longhands
       <td>no
    </table>
    <p>This property specifies the background position’s inline-axis component.
-	An omitted origin keyword is assumed to be <a class="css" data-link-type="maybe" href="https://drafts.csswg.org/css-transitions-1/#valdef-steps-start">start</a>.</p>
+	An omitted origin keyword is assumed to be <span class="css">start</span>.</p>
    <table class="def propdef" data-link-for-hint="background-position-block">
     <tbody>
      <tr>
@@ -379,7 +379,7 @@ <h4 class="heading settled" data-level="2.1.1" id="background-position-longhands
       <td>no
    </table>
    <p>This property specifies the background position’s block-axis component.
-	An omitted origin keyword is assumed to be <a class="css" data-link-type="maybe" href="https://drafts.csswg.org/css-transitions-1/#valdef-steps-start">start</a>.</p>
+	An omitted origin keyword is assumed to be <span class="css">start</span>.</p>
    <h2 class="heading settled" data-level="3" id="corners"><span class="secno">3. </span><span class="content"> Corners</span><a class="self-link" href="#corners"></a></h2>
    <h3 class="heading settled" data-level="3.1" id="corner-sizing"><span class="secno">3.1. </span><span class="content"> Corner Sizing: the 'border-radius property</span><a class="self-link" href="#corner-sizing"></a></h3>
    <table class="def propdef" data-link-for-hint="border-radius">
@@ -1031,7 +1031,6 @@ <h3 class="no-num no-ref heading settled" id="index-defined-elsewhere"><span cla
     <a data-link-type="biblio">[css-transitions-1]</a> defines the following terms:
     <ul>
      <li><a href="https://drafts.csswg.org/css-transitions-1/#funcdef-transition-timing-function-cubic-bezier">cubic-bezier()</a>
-     <li><a href="https://drafts.csswg.org/css-transitions-1/#valdef-steps-start">start</a>
     </ul>
    <li>
     <a data-link-type="biblio">[css-values]</a> defines the following terms: