/* for low resolution display */
img.PaginaWeb-20-20 {
    background-image: url(../../imagens/PaginaWeb);
    background-repeat: no-repeat;
    background-size: px 20px;
}
/* for high resolution display */
@media only screen and (min--moz-device-pixel-ratio: 1.5),
only screen and (-o-min-device-pixel-ratio: 3/2),
only screen and (-webkit-min-device-pixel-ratio: 1.5),
only screen and (min-device-pixel-ratio: 1.5) {
img.PaginaWeb-20-20 {
    background-image: url(../../imagens/PaginaWeb@2x);
    background-repeat: no-repeat;
    background-size: 20px 20px;
}
}