.lookupInput a{
                position: absolute;
                width: 33px !important;
                margin-left: 5px;
                background-image: url(/img/setup/search-icon.png) !important;
                background-repeat: no-repeat !important;
                background-position: center !important;
              display: inline-flex !important;
            }
            .lookupInput input{
                width:91% !important;
            }
            .lookupInput a img{
                display:none !important;
            }

styleClass="slds-lookup__search-input slds-input"