There was a time when the only way to get nice 1px borders was to place your tab...

rimliu on June 6, 2019 | parent | context | favorite | on: CSS Grid Level 2 – subgrid is coming to Firefox

There was a time when the only way to get nice 1px borders was to place your table inside the other table, set the outer table's cell to the color you wanted for your background and then set cellspacing on the inner table to 1px.