Spacing between thead and tbody

Answer 1

This will give you some white space between the header and table content

thead tr {
  border-bottom: 10px solid white;
}

Although setting the border colour is a bit of a cheat method, it will work fine.

Form investigation, you can't set box-shadow to a table row, but you can to table cells:

th {
  box-shadow: 5px 5px 5px 0px #000000 ;
}

(I'm not sure how you want the shadow to look like, so just adjust the above.)