misc: common.css를 bootstrap5를 포함한 css로 변경

hwe/scss/game_bg.scss

@@ -1,5 +1,3 @@
-@charset "UTF-8";
-
 @import url('https://fonts.googleapis.com/css2?family=Nanum+Gothic:wght@400;700&display=swap');
 @import '../../d_shared/common.css';