change header color background

Hi,

The theme i want to use is "Tech" and i not successful to change the header color, i've tried to search in style.css or in the css directory but i only succeeded to change the background below

/*------------------------------ PAGE ------------------------------*/
@import url(css/font.css);

html {
	background:#3b2957;
}

can someone help me?
p.s. sorry for bad english

ok that was an image : "top.png", i just modified it