the index page of gii doesn't work fine....lack of css style : [something wrong with index][1]


it doesn't work out.the success one is like this:
[the correct one][2]


the config of nginx is right.so, why can't I see the page with correct css style?
I'm new to yii,so please help me at your convenience


  [1]: https://i.stack.imgur.com/Ca9vr.png
  [2]: https://i.stack.imgur.com/CC1TR.png