Just discovered how to lose the gap between cells and the table itself - so you can get a single line everywhere. The trick is:

border-collapse: collapse;



table.jtable {
width: 90%;
background-color: #ffffff;
margin-left: auto;
margin-right: auto;
border-collapse: collapse;

}

table.jtable th {
background-color: #999900;
padding: 5px;
margin: 0px;
border: solid 1px #000000;
}

table.jtable td {
background-color: #ffffff;
padding: 5px;
margin: 0px;
border: solid 1px #000000;
}