.hide {
    display: none;
}
@media(max-width:768px) {
    th.gm, td.gm, tr.gm {
        display: block;
    }

    /* Hide table headers (but not display: none;, for accessibility) */
    thead tr {
        position: absolute;
        top: -9999px;
        left: -9999px;
    }

tr {
  margin: 0 0 1rem 0;
}
  
tr:nth-child(odd) {
  background: #ccc;
}

    td {
        /* Behave  like a "row" */
        border: none;
        border-bottom: 1px solid #eee;
        position: relative;
        padding-left: 50%;
    }

    td:before {
        /* Now like a table header */
        position: absolute;
        /* Top/left values mimic padding */
        top: 11px;
        left: 6px;
        width: 45%;
        padding-right: 10px;
        white-space: nowrap;
    }

    .hide {
        display:block;
    }
    /*
    Label the data
You could also use a data-* attribute and content for this. That way "bloats" the HTML, this way means you need to keep HTML and CSS in sync. Lea Verou has a clever way to handle with text-shadow.
    */
    td.gm:nth-of-type(1):before { content: "Date:"; }
    td.gm:nth-of-type(2):before { content: "Mileage:"; }
    td.gm:nth-of-type(3):before { content: "Trip Miles:"; }
    td.gm:nth-of-type(4):before { content: "Gallons:"; }
    td.gm:nth-of-type(5):before { content: "Gas Mileage:"; }
    td.gm:nth-of-type(6):before { content: "Cost/Gallon:"; }
    td.gm:nth-of-type(7):before { content: "Total:"; }
}