.x-toolbar .gx-map-measurelength {
    background: url('../images/ruler.png') top left no-repeat;
}
.x-toolbar .gx-map-measurearea {
    background: url('../images/ruler_square.png') top left no-repeat;
}
.x-toolbar .gx-map-measureposition {
    background: url('../images/bullet_orange.gif') top left no-repeat;
}