Css style is lose

Hi,
I have a login page with a css style and it works in the internet explorer.
But, when a put the authentication tags in the web.config, the page lose the css style. Why it happening.
There is my authentication tags:
<authentication mode="Forms">
<forms loginUrl="/GlobalCLient/frmLogin.aspx"
  protection="All"
  timeout="5"
  name=".ASPXAUTH"
  path="/"  
  requireSSL=&qu ...