I notice that you are trying to scroll the form in narrow devices but {overflow:scroll} is on the wrong box. Move it down to
.createSubAdminBlock {
overflow:scroll;
...
and the form will scroll horizontally in narrow devices… if that is what you want.
Unrelated: the nested table must be within a parent table cell, not a table row. What you have now is invalid.
<div class="createSubAdminBlock">
<table>
<tr>
<td> <!-- ADD Me here and elsewhere where neede -->
<table>
<tr>
<td class="tableHeader">CreateIDFor</td>
...
I have never come across a situation where tabular data contained more tabular data in individual cells that actually made sense when presented as nested tables. A question for the person trying to nest the tables is - Are you sure that you have one of the rare one in a trillion exceptions where nesting tables actually makes sense both to the reader and semantically?
I agree completely. My strategy was to go from a known state to a stable state with balanced tags (always a basic need) and then introduce better framing (without the parent table) as a next step. That was my rationale for not talking about the outer table right away. Since @vngx has not returned, “2 discreet steps instead of 1 more involved step” may have been a weak decision. It was a judgement call.
@vngx, if you are still reading this, in the following example I removed the outer table from your code. I also replaced the <hr ...> horizontal line by applying {margin-top} to the second table. There is NO significant difference in the way the page looks and behaves.
The CSS that adds the margin above the second table: