CSS for Table Rows and Columns

After much frustration I realised that the issue is the fact that you need ultimately to specify what you do with the cell in the nth row, hence the correct code is:

table td:nth-child(1),
table tr:nth-child(1) td {
  font-weight: bold;
}

Putting this up as the answer as there are a lot of sources that use the header to style the top row but don’t stipulate what needs to be done if you have a table layout without a header.