diff --git a/css/chess.css b/css/chess.css
index bff0420..a175e70 100644
--- a/css/chess.css
+++ b/css/chess.css
@@ -25,6 +25,7 @@ button:disabled .silhouette {
 #cb_outer {
    width: 100%;
    max-width: calc(100vh - 4em);
+   flex: 1 0 auto;
 }
 
 #cb_container {