fix: clarify order of values for border shorthand

Author: vwkd

css-backgrounds-3/Overview.bs

@@ -1416,11 +1416,21 @@ color ('border-color'), and thickness ('border-width') of the border.
 <p>These properties set the foreground color of the border specified
 by the <span class=property>border-style</span> properties.
 
-<p>'Border-color' is a shorthand for the
-four 'border-*-color' properties. The four values set the top, right,
-bottom and left border, respectively. A missing left is the same as
-right, a missing bottom is the same as top, and a missing right is
-also the same as top.
+<p>The 'border-color' property is a shorthand property for setting
+'border-top-color', 'border-right-color', 'border-bottom-color', and 'border-left-color'
+in a single declaration.
+
+<p>If there is only one component value,
+it applies to all sides.
+If there are two values,
+the top and bottom are set to the first value
+and the right and left are set to the second.
+If there are three values,
+the top is set to the first value,
+the left and right are set to the second,
+and the bottom is set to the third.
+If there are four values
+they apply to the top, right, bottom, and left, respectively.