.mainTbl td:nth-child(2), .mainTbl th:nth-child(2) {
    min-width: 300px;
    white-space: normal;
}

@media only screen and (max-width:480px) {
    .mainTbl td:nth-child(2), .mainTbl th:nth-child(2) {
        min-width: auto;
        white-space: nowrap;
    }
}