I want to put triple border of 3 different colors in a single div as because the design is like this. Please help me out by solving the problem.

You can only have one border-color (on each side) of an element. To get three colors you might nest three elements inside each other.

Or you could use images and make a single border look like whatever you want.

Rounded corners and shadowed boxes
Creating Custom Corners & Borders
Creating Custom Corners & Borders Part II