LibWeb: Implement `@supports` rule :^)

The main thing missing is that we don't serialize the supports clause,
but for actually using a `@supports (something: cool) {}` rule in CSS,
it works!

1 files changed, 1 insertions, 0 deletions

diff --git a/Userland/Libraries/LibWeb/Forward.h b/Userland/Libraries/LibWeb/Forward.h
index cdc6d6a33b..4d01a66e97 100644
--- a/Userland/Libraries/LibWeb/Forward.h
+++ b/Userland/Libraries/LibWeb/Forward.h
@@ -26,6 +26,7 @@ class CSSRuleList;
 class CSSStyleDeclaration;
 class CSSStyleRule;
 class CSSStyleSheet;
+class CSSSupportsRule;
 class Display;
 class ElementInlineCSSStyleDeclaration;
 class Length;