setting focus & chaning bg color

i have a  application in asp.net. few of the pages are like registration pages with few controls, like textbox, dropdown etc..

wht i want is when the page is loaded the focus shld be on the first control  and as and when the controls receives focus its background colur shld change and on lostfocus t shld gain change

at present i am uisng txtname.focus() in the code behind for setting focus to the first control
and using javascript making the color chnage , but i am getting error if i use both
. how do i set it in code behind?????

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