• Each column and row can be styled differently using the class selection:

td {border:solid blue 2pt}
th {border:solid red 1pt}
table {border:dotted green 3pt;  border-collapse:collapse}
tr.one {background-color:white}
tr.two {background-color:pink}
tr.three {background-color:navajowhite}
colgroup.a {background-color:yellow}
colgroup.b {background-color:lime}
. . .
<colgroup class="a" span="2" />
<colgroup class="b" span="3" />
. . .

The first two columns are styled different from the last three but only the parts seen through the transparent row are visible