javascript - HTML table is not acting as supposed

Question

I'm trying to create basic chat using ASPX and HTML. The output itself is fine but the problem is that the table just keeps growing and growing. I want it to be scrollable instead. Here's what I tried and its not working:

<td style="height: 100px">
    <div style="overflow:scroll;display:block">
        <%=output %>
    </div>
</td>