Position sticky on thead th works in 2018!
In your stylesheets just add this one line:
thead th { position: sticky; top: 0; }
Your table will need to include thead and th for this to style.
<table>
<thead>
<tr>
<th>column 1</th>
<th>column 2</th>
<th>column 3</th>
<th>column 4</th>
</tr>
</thead>
<tbody>
// your body code
</tbody>
</table>
Also, if you have multiple rows in thead, you can select the first one to remain sticky:
thead tr:first-child th { position: sticky; top: 0; }
As of March 2018 support is pretty much there across modern browsers
ref: https://caniuse.com/#feat=css-sticky
Credit goes to @ctf0 for this one (ref comment made 3 Dec 2017)