how change the gray background ?

body {
    font-size: 62.5%;
    background: #fff;
    font-family: "Lucida Grande",Verdana,"Bitstream Vera Sans",Arial,sans-serif;
    line-height: 22px;
    color: #555;
    margin-bottom: 40px;

not sure what gray background you are talking about

I made print screen to get clear what I mean sir
https://img823.imageshack.us/img823/8683/92263851.png

thank you

white background:

#wrapper {
background: #fff; // Change this
margin-top: 0px;
padding: 0 0px;

}

For changing gray background via css,
edit
body {
background: #f1f1f1;
}

great !

thank you so much