django网站中二级目录下的网页打开后没有CSS样式

不是admin后台的样式（这个网上有解决问题）。
而是这样比如：abc.com/blog/create或abc.com/news/add这样在create和add页面中没有css样式，我觉得是urls.py的问题，但不知具体怎么错了，代码如下，有一个主目录urls.py，另外两个是blog和news应用下的urls.py文件

// 主目录的urls.py
from django.conf.urls import patterns, include, url
from django.contrib import admin
from django.contrib.auth.views import login,logout     
urlpatterns = patterns('',
    # Examples:
    url(r'^blog/', include('blog.urls')),
    url(r'^news/',include('news.urls')),
)

//news/urls.py
from django.conf.urls import patterns, include, url

urlpatterns = patterns('news.views',
    url(r'^$','news_list'),
    url(r'add/$','add_news'),
)

//blog/urls.py
from django.conf.urls import patterns, include, url
from blog.views import create_topic

urlpatterns = patterns('blog.views',
    url(r'^$','topic_list'),
    url(r'^create/$','create_topic'),
)