refactor(docs\*.css): refactor css code style

docs/templates/index.jade

@@ -22,7 +22,7 @@ block content
                 span.demo-link-label Demo
   div.index-block
     div.wrap
-      h1 Why ng2-admin?
+      h1.centered Why ng2-admin?
       div.why-items
         div.why-item
           img(src=contents.images['why-structure.svg'].url)
@@ -36,23 +36,23 @@ block content
           img(src=contents.images['why-practices.svg'].url)
           h4 Ease of customization
           p Check out #[a(href='/ng2-admin/articles/011-changing-color-scheme') our article], where we describe how you can create different look in just 2 minutes!
-  div.index-block.black
+  div.index-block
     div.wrap
-      h1 Is it free?
+      h1.centered Is it free?
       p Yes, ng2-admin is completely free and MIT licensed. That means you can do with it whatever you want.
 
   div.index-block
     div.wrap
-      h1 How can I support you guys?
+      h1.centered How can I support you guys?
       p Here's what you can do:
       ul
         li Star #[a(href='https://github.com/akveo/ng2-admin',target='_blank') our GitHub repo]
         li Create pull requests, submit bugs, suggest new features
         li Follow #[a(href='https://twitter.com/akveo_inc',target='_blank') us on Twitter]
         li Like #[a(href='https://www.facebook.com/akveo/',target='_blank') our page on Facebook]
-  div.index-block.black
+  div.index-block
     div.wrap
-      h1 Can I hire you?
+      h1.centered Can I hire you?
       p Yes! We are available for hire. Visit #[a(href='http://akveo.com',target='_blank') our homepage]
         | or simply leave us a note at #[a(href='mailto:contact@akveo.com') contact@akveo.com].
         | We will be happy to work with you!