I would avoid styling tr elements because they don't really "exist" as such, apart from for semantic reasons. You're better off targeting the table cells themselves, with something like this:
table tfoot tr:first-child th,
table tfoot tr:first-child td {
font-weight:bold;
background:yellow;
border-top:2px solid red;
border-bottom:2px solid red;
}
Also, since you are targeting directly nested elements, you can use the child selector, which is faster for browsers to parse (they only have to search one level up/down).
table > tfoot > tr:first-child > th,
table > tfoot > tr:first-child > td {
...
}
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