.zi {
    width: 20px;
    height: 20px;
    border: none;
    display: inline-block;
    font-size: inherit;
    text-rendering: auto;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    background-size: cover;
    background-repeat:  no-repeat;
}

.zi-bus {    background-image: url("zi/bus.png");}
.zi-avia{    background-image: url("zi/avia.png");}