input.button-add {
height: 32px;
padding-left: 36px;
padding-right: 10px;
border: 1px solid #000000;
background: #ff9900 url("http://placehold.it/16x16") no-repeat 10px center;
cursor: pointer;
}
background-image: url(...);
background-repeat: no-repeat;
background-position: <left|right>;
padding-<left|right>: <width of image>px;