make 6 a valid length for hex colors

Also marks `isHexColor` as public function.

Author: nikneym

src/browser/cssom/CSSStyleDeclaration.zig

@@ -190,7 +190,7 @@ fn isNumericWithUnit(value: []const u8) bool {
     return CSSKeywords.isValidUnit(unit);
 }
 
-fn isHexColor(value: []const u8) bool {
+pub fn isHexColor(value: []const u8) bool {
     if (value.len == 0) {
         return false;
     }
@@ -199,7 +199,7 @@ fn isHexColor(value: []const u8) bool {
     }
 
     const hex_part = value[1..];
-    if (hex_part.len != 3 and hex_part.len != 6 and hex_part.len != 8) {
+    if (hex_part.len != 3 and hex_part.len != 4 and hex_part.len != 6 and hex_part.len != 8) {
         return false;
     }