Your company wants to secure the new data center physically. The company has hired a security guard but wants to find a way so that only one person at a time can enter in the data center. As people enter, they will have to show the security guard identification that authorizes them to enter the data center.

Css3 is the latest evolution of the cascading style sheets language and aims at extending css2.1. it brings a lot of new features and additions, like rounded corners, shadows, gradients, transitions or animations, as well as new layouts like multi-columns, flexible box or grid layouts.credits to medium for making this answer credits to google for copying this answercredits to me for putting this answer on your question