[css-syntax] Specify that duplication declarations in style rules are discarded.

Author: tabatkins

css-syntax/Overview.html

@@ -2770,6 +2770,9 @@ <h3 data-level=8.1 id=style-rules><span class=secno>8.1 </span><span class=conte
 	The validity of the style rule’s contents have no effect on the validity of the style rule itself.
 	Unless otherwise specified, property names are <a href=#ascii-case-insensitive>ASCII case-insensitive</a>.
 
+<p>	If a <a href=#style-rule>style rule</a> contains multiple declarations with the same name,
+	all but the last such declaration are discarded.
+
 <p class=note>	Note: The names of Custom Properties <a data-biblio-type=informative data-link-type=biblio href=#css-variables title=CSS-VARIABLES>[CSS-VARIABLES]</a> are case-sensitive.
 
 <p>	<a href=#qualified-rule>Qualified rules</a> at the top-level of a CSS stylesheet are style rules.

css-syntax/Overview.src.html

@@ -2657,6 +2657,9 @@ <h3>
 	The validity of the style rule’s contents have no effect on the validity of the style rule itself.
 	Unless otherwise specified, property names are <i>ASCII case-insensitive</i>.
 
+	If a <i>style rule</i> contains multiple declarations with the same name,
+	all but the last such declaration are discarded.
+
 	Note: The names of Custom Properties [[CSS-VARIABLES]] are case-sensitive.
 
 	<i>Qualified rules</i> at the top-level of a CSS stylesheet are style rules.