Here Mudassar Ahmed Khan has explained, how to change the background color style of TextBox on focus i.e. Highlight TextBox on focus and set it back to default on blur
There is absolutely no need of using jQuery, JavaScript or ASP.Net scripts for this purpose as the solution provided explains how to use pure CSS styles to change the background color style of TextBox on focus.
Since CSS is involved we can easily Highlight TextBox by change its Border style or color too instead of changing the Background color style.
Advantage of using CSS is that it will work for all technologies i.e. ASP.Net, HTML, PHP, JSP, etc. without writing a single line of jQuery or JavaScript and also is cross browser compatible.