Dear Jack,
The built-in HTML action is only for the horizontal table not the vertical table and the CSS example code is generally applied to the horizontal table.
You may use the custom html code to see the result.
Here is the example code.
<style>
table {
border-collapse: collapse;
}
td {
border: 1px solid black;
padding: 5px;
}
td:first-child {
font-weight: bold;
}
td:nth-child(2) {
border-left: none;
}
</style>
<table>
<tbody>
<table border="1" class="variant-table" >
<tr>
<td style="background-color: #53B3AE;">TypeColumn</td>
<td>@{outputs('Get\_item')?['body/TypeColumn/Value']}</td>
</tr>
<tr>
<td style="background-color: #53B3AE;">LocationColumn</td>
<td>@{outputs('Get\_item')?['body/LocationColumn/Value']}</td>
</tr>
<tr>
<td style="background-color: #53B3AE;">DepartmentColumn</td>
<td>@{outputs('Get\_item')?['body/DepartmentColumn/Value']}</td>
</tr>
</tbody>
</table>

Flow:



Result:

Welcome to share any updates at your convenience.
Thank you for your effort and time.
Sincerely
Cliff | Microsoft Community Moderator