how to reduce height of this html text box ?

Increasing the font size on a text box will usually expand its size automatically.

<input type="text" style="font-size:16pt;"></input>

If you want to set a height that is not proportional to the font size, I would recommend using something like the following. This prevents browsers like IE from rendering the text inside at the top rather than vertically centered.

.form-text{
    padding:15px 0;
}</pre>