CSS Table formatting with multiple items in one td

Question

So I am working on a form. And part of how I want the form to function requires a select box and an input(text) box in the same tr. The other items in that tr are just text boxes. I am having a problem getting the text box that shares a tr with the select to go to where the solo text box goes. Therefore, the right edges do not line up.

What I am looking for...

1) I want the text boxes that are solo to fill the box, ideally without adding width. I am fine with a min width of 550px, but not necessary.

2) I want the text boxes that are with the select to fill the rest of the box, meeting the same edge as the solo boxes. Satisfying OCD...

CSS for the table:

table, th, td {
    border: 1px solid var(--main-color);
    padding: 6px 8px;
    white-space: nowrap;
}

table {
    border-collapse: collapse;
    table-layout: fixed;
}

thead {
    background-color: #333;
    border-bottom: 3px solid var(--main-color);
}

thead th, thead a, thead a:visited {
    color: white;
}

th.active {
    background: var(--main-color);
}

table > :not(thead) tr th {
    background-color: #333;
    border-right: 3px solid var(--main-color);
    color: white;
    text-align: right;
}

tr {
    height: auto;
}

td {
    color: black;
}

table input {
        width:100%; /* simply scale inputs to table cell size */
    }
        td.input-group input {
            width:auto; /* but not for radios or checks */ 
        }

HTML (shortened, just one solo text box and one that is sharing with the select):

<table>
    <tr>
        <td>Serial Number: </td>
        <td><input type="text" name="device-serial-number" maxlength="8" required></td>
    </tr>

    <tr>
        <td>MAC Address NIC: </td>
        <td>
            <select name="media-nic">
                <option value="">Media</option>
                <option value="eth">Ethernet</option>
                <option value="inf">Infiniband</option>
                <option value="fib">Fiber</option>
            </select>

            <input type="text" name="mac-nic" maxlength="17">
        </td>
    </tr>
</table>

Fiddle with more CSS and such: https://jsfiddle.net/2o0sn4ep/

Answer 1

You could use the trick marked as correct answer in this question

Using this nice "trick" I modified a bit your css and html (I added a div container to wrap your second input).

It's responsive as well, your inputs will always fill whatever width remaining in the container

:root {
  --main-color: rgb(46, 58, 150);
}

* {
  box-sizing: border-box;
}

table,
th,
td {
  border: 1px solid var(--main-color);
  padding: 6px 8px;
  white-space: nowrap;
}

table {
  border-collapse: collapse;
  table-layout: fixed;
}

thead {
  background-color: #333;
  border-bottom: 3px solid var(--main-color);
}

thead th,
thead a,
thead a:visited {
  color: white;
}

th.active {
  background: var(--main-color);
}

table >:not(thead) tr th {
  background-color: #333;
  border-right: 3px solid var(--main-color);
  color: white;
  text-align: right;
}

tr {
  height: auto;
}

td:first-child {
  text-align: right;
}

td {
  color: black;
}

input[type=text] {
  padding: 9px 10px;
  font-size: 16px;
  width: 100%;
}

select {
  padding: 9px 10px;
  font-size: 16px;
  height: 41px;
  float: left;
  margin-right: 5px;
}

option {
  padding-top: 2px;
  padding-bottom: 2px;
}

div {
  width: auto;
  overflow: hidden;
}

<table>
  <tr>
    <td>Serial Number: </td>
    <td>
      <input type="text" maxlength="8" required>
    </td>
  </tr>

  <tr>
    <td>MAC Address NIC: </td>
    <td>
      <select>
        <option value="">Media</option>
        <option value="eth">Ethernet</option>
        <option value="inf">Infiniband</option>
        <option value="fib">Fiber</option>
      </select>
      <div>
        <input type="text" maxlength="17">
      </div>



    </td>
  </tr>
</table>