Is there any common CSS library?

I'm looking for CSS library that hold all common css best practices.

For example block centering style:

.block-center {
   margin-left : auto;
   margin-right : auto;
}

<div class="myClass block-center" />

I want such library to be distributed as separate css file which I can add and use in my projects.

I think you mean CSS framework: there are tons of them. Just to name a few:

• Blueprint
• BlueTrip
• Boilerplate
• Content with Style
• Elastic
• Elements
• Mollio
• 960 Grid System
• 1KB Grid
• SenCSs
• Tripoli
• Typogridphy
• YAML
• YUI Grids

Everyone and their mother has a CSS Framework: there is no best one, and they all have their own interpretation of what constitutes "best practices". it really depends on what one fits your own use.

Also see bobince's answer on What is the best CSS Framework and are they worth the effort? for why CSS Frameworks are really unnecessary.

You should try using Twitter Bootstrap, it is very easy to use, there are many YouTube tutorials.

I stopped using other CSS methods after finding out about it.