diff --git a/System/Libraries/Css/Tokenizer.HC b/System/Libraries/Css/Tokenizer.HC
index 0161c72..5efd92e 100644
--- a/System/Libraries/Css/Tokenizer.HC
+++ b/System/Libraries/Css/Tokenizer.HC
@@ -20,6 +20,12 @@
 #define CSS_DISTANCE_PERCENT 3
 #define CSS_DISTANCE_AUTO 4
 
+#define CSS_SIDE_UNDEFINED 0
+#define CSS_SIDE_TOP 1
+#define CSS_SIDE_RIGHT 2
+#define CSS_SIDE_BOTTOM 3
+#define CSS_SIDE_LEFT 4
+
 #define CSS_TEXT_ALIGN_LEFT 0
 #define CSS_TEXT_ALIGN_CENTER 1
 #define CSS_TEXT_ALIGN_RIGHT 2