While setting the new Git server with gitweb I saw this issue.Generally never seen before,here Gitweb page was not displaying correctly.

You can see the below given screenshot:

While debugging the issue,it is found that the problem was with MIME for css and javascript.
To solve this issue ,I only approached to create a .htaccess file in Data Directory of gitweb.
In CentOS the gitweb directory I created inside /var/www/gitweb.

You have to add only these two lines in .htaccess

[root@localhost gitweb]# vi .htaccess 
AddType text/css .css
AddType text/javascript .js
[root@localhost gitweb]#

Now restart the apache once and clear the web browser cache also

/etc/init.d/httpd restart