Change post-detail.html to inherit base.html schema

[akikodesu]

I made the post-detail page inherit the structure and styles from base files for following reasons:

1. to facilitate the maintenance of their own written modules
2. To make it easier for the person in charge of base.html and base.css not to be disturbed by other parts of the code.

And add some adaptive code, the actual effect still need to be decided according to the test.