Sticky/Fixed Header

I’m trying to have the thead be fixed on scroll, but it doesn’t seem to work with any code that I do. The closest I got was

table tbody, table thead {
display: block;
}

table tbody {
overflow:auto;
height: 800px;
}

But when I do that all of the rows are misaligned with the header. Any suggestions?

https://www.ads-software.com/plugins/footable/