CSS broken when the site is loading


I am using OJS, due to some unknown issue its not loading the default Stylesheet when the site si loding. I added a custom style sheet from Admin at Settings > Website > Appearance: Journal style sheet. after adding this css file site works fine but when the site is loading is showing everything is broken for a while (about 1sec or less) due to missing the default CSS. After loading complete the site become OK.

My Site URL is : http://www.bdpsjournal.org/index.php/bjp

Can anyone help?