Fix User Guide CSS Issue

- Fix Search Button CSS Issue with Safari, make compatible with all major web browsers:
    - Tested in following browsers: IE8+, FF3+, Chrome 14+, Safari4+, Opera10+, iOS, OS X, Android Browser
- Add a space between Header and `headerlink` (relative to header `font-size`).

**[Live Demo](http://qolami.com/CodeIgniter/)**

Signed-off-by: Hashem Qolami <hashem@qolami.com>