@rahulephp
First, I have moved your thread over here to the HTML/CSS forums. Since this is obviously a CSS question, it did not belong in the PHP forum. You need to please be sure and post your question under the most appropriate forum topic next time.... please.
As for your question, what do you want to change? The input area will be blank until the user enters something. But, if you want to play with it to see if you can change it prior to the user entering anything (which I haven't tried or worried about before), you should add a class name to your input link and then, in your CSS play with the different attributes relating to font.
Its not that I am unwilling to show you, but if you don't yet know CSS, then you really need to learn it and there is no time like the present when you need to do something, to learn it.
Regards,
Jeff