allow optional alpha channel in rgb()

match browsers, which don't distinguish rbg() vs rgba()

Author: dwarring

lib/CSS/Grammar.rakumod

@@ -86,10 +86,11 @@ grammar CSS::Grammar:ver<0.3.10> {
     rule end-decl        { ';' | <?before '}'> | $ }
 
     rule color-range     { <num>[$<percentage>=\%]? }
+    rule alpha-value     { <num>[$<percentage>=\%]? }
 
     proto rule color     {*}
     rule color:sym<rgb>  {:i 'rgb('
-			      [ <color-range> **3% ',' || <any-args> ]
+			      [ <color-range> **3% ',' [ ',' <alpha-value> ]? || <any-args> ]
                                 ')'
                          }
     rule color:sym<hex>  { <id> }

lib/CSS/Grammar/Actions.rakumod

@@ -192,6 +192,14 @@ class CSS::Grammar::Actions {
         make $.build.token( $range.round, :type(CSSValue::NumberComponent));
     }
 
+    method alpha-value($/) {
+        my $alpha = $<num>.ast.value;
+        $alpha /= 100
+            if $<percentage>;
+        $alpha = min( max($alpha, 0), 1);
+        make $.build.token( $alpha.round(.01), :type(CSSValue::NumberComponent));
+    }
+
     proto method color {*}
     method color:sym<rgb>($/)  {
         return $.warning('usage: rgb(c,c,c) where c is 0..255 or 0%-100%')