Css: Fix tests

It's not easy to find a CSS property that is implemented even in
ancient browsers and that returns a consistent result among browsers
when passed through .css(). color didn't work since Firefox normalizes
it an empty value to rgb(0, 0, 0).

(cherry-picked from 0c12cb39)

test/unit/css.js

@@ -988,16 +988,19 @@ test( "Keep the last style if the new one isn't recognized by the browser (#1483
 	expect( 2 );
 
 	var el;
-	el = jQuery( "<div></div>" ).css( "color", "black" ).css( "color", "fake value" );
-	equal( el.css( "color" ), "black", "The old style is kept when setting an unrecognized value" );
-	el = jQuery( "<div></div>" ).css( "color", "black" ).css( "color", " " );
-	equal( el.css( "color" ), "black", "The old style is kept when setting to a space" );
+	el = jQuery( "<div></div>" ).css( "position", "absolute" ).css( "position", "fake value" );
+	equal( el.css( "position" ), "absolute", "The old style is kept when setting an unrecognized value" );
+	el = jQuery( "<div></div>" ).css( "position", "absolute" ).css( "position", " " );
+	equal( el.css( "position" ), "absolute", "The old style is kept when setting to a space" );
 });
 
 test( "Reset the style if set to an empty string", function() {
 	expect( 1 );
-	var el = jQuery( "<div></div>" ).css( "color", "black" ).css( "color", "" );
-	equal( el.css( "color" ), "", "The style can be reset by setting to an empty string" );
+	var el = jQuery( "<div></div>" ).css( "position", "absolute" ).css( "position", "" );
+	// Some browsers return an empty string; others "static". Both those cases mean the style
+	// was reset successfully so accept them both.
+	equal( el.css( "position" ) || "static", "static",
+		"The style can be reset by setting to an empty string" );
 });
 
 asyncTest( "Clearing a Cloned Element's Style Shouldn't Clear the Original Element's Style (#8908)", 24, function() {