[css-borders-4] Fixed and added definitions for box-shadow-offset: none (#9096)

Fixed and added definitions for `box-shadow-offset: none` and the expansion of the `box-shadow` shorthand

Author: SebastianZ

css-borders-4/Overview.bs

@@ -622,16 +622,25 @@ Initial: none
 Applies to: all elements
 Inherited: no
 Percentages: N/A
-Computed value: either 'none' or a list,
-	each item a pair of offsets (horizontal and vertical) from the element‘s box
-Animation type: by computed value
+Computed value: list, each item either 'none' or a pair of offsets
+  (horizontal and vertical) from the element‘s box
+Animation type: by computed value,
+  treating ''box-shadow-offset/none'' as ''0 0''
+  when interpolated with non-'none' values.
 </pre>
 
 <p>The 'box-shadow-offset' property defines one or more drop shadow offsets.
-The property accepts a comma-separated list of horizontal and vertical offset pairs,
+The property accepts a comma-separated list.
+Each item in that list can either be the ''box-shadow-offset/none'' value,
+which indicates no shadow, or a pair of horizontal and vertical offsets,
 where both values are described as <<length>> values.
 
 <dl>
+  <dt><dfn id="shadow-offset-none">none</dfn>
+  <dd>
+    The shadow will not be rendered.
+    The values of other box shadow properties corresponding to this shadow have no effect.
+
   <dt><dfn id="shadow-offset-x">1st <<length>></dfn>
   <dd>
     Specifies the <dfn>horizontal offset</dfn> of the shadow.
@@ -746,25 +755,21 @@ Initial: none
 Applies to: all elements
 Inherited: no
 Percentages: N/A
-Computed value: either the keyword ''box-shadow-offset/none'' or
-    a list, each item consisting of four absolute lengths
-    plus a computed color and optionally also a ''box-shadow-position/inset'' keyword
-Animation type: by computed value,
-    treating ''box-shadow-offset/none'' as a zero-item list
-    and appending blank shadows (''transparent 0 0 0 0'')
-    with a corresponding ''box-shadow-position/inset'' keyword as needed
-    to match the longer list
-    if the shorter list is otherwise compatible with the longer one
+Computed value: see individual properties
+Animation type: see individual properties
 </pre>
 
   <p>The 'box-shadow' property attaches one or more drop-shadows to the box.
-  The property accepts either the ''box-shadow-offset/none'' value, which indicates no shadows,
-  or a comma-separated list of shadows, ordered front to back.
+  The property accepts a comma-separated list of shadows,
+  ordered front to back.
 
   <p>Each shadow is given as a <<spread-shadow>>,
   outlining the 'box-shadow-offset', and optional values for the 'box-shadow-blur',
   'box-shadow-spread', 'box-shadow-color', and 'box-shadow-position'.
-  Omitted lengths are 0; omitted colors default to the ''currentcolor'' value.
+  Omitted lengths are '0';
+  omitted colors default to ''transparent'' when the specified offset is ''box-shadow-offset/none''
+  and to ''currentcolor'' otherwise.
+
   <pre class=prod>
   <dfn><<spread-shadow>></dfn> = <<'box-shadow-color'>>? &amp;&amp; [ <<'box-shadow-offset'>> [ <<'box-shadow-blur'>> <<'box-shadow-spread'>>? ]? ] &amp;&amp; <<'box-shadow-position'>>?</pre>