diff --git a/_theme.json b/_theme.json
index 3a5a6bfa..e4a3cf68 100644
--- a/_theme.json
+++ b/_theme.json
@@ -86,7 +86,8 @@
 			}
 		},
 		"background": {
-			"backgroundImage": true
+			"backgroundImage": true,
+			"backgroundSize": true
 		}
 	}
 }
\ No newline at end of file
diff --git a/readme.txt b/readme.txt
index d31d98e4..a0ee83fd 100644
--- a/readme.txt
+++ b/readme.txt
@@ -38,6 +38,7 @@ https://www.vektor-inc.co.jp/inquiry/
 
 == Changelog ==
 
+[ G3 ][ 6.5 ] Attend to backgroundSize
 [ G3 / G2 ] Allow using CSS level 4 viewport-relative units
 
 v15.20.2