Allora puoi usare il selettore nth-child().
Esempio pratico:
codice:
<!DOCTYPE HTML>
<html>
<head>
<title>Esempio</title>
<meta charset="utf-8">
<style type="text/css">
table{
width:300px;
border-collapse:collapse;
}
table tr td{
border:1px solid Grey;
}
table tr{ /* tutte le altre righe */
background:Beige;
}
table tr:nth-child(1){ /* la prima riga */
background:Green;
}
table tr:nth-child(2){ /* la seconda riga */
background:Yellow;
}
table tr:nth-child(20){ /* la ventesima riga */
background:Red;
}
</style>
</head>
<body>
<table>
<tr><td>1</td><td></td></tr>
<tr><td>2</td><td></td></tr>
<tr><td>3</td><td></td></tr>
<tr><td>4</td><td></td></tr>
<tr><td>5</td><td></td></tr>
<tr><td>6</td><td></td></tr>
<tr><td>7</td><td></td></tr>
<tr><td>8</td><td></td></tr>
<tr><td>9</td><td></td></tr>
<tr><td>10</td><td></td></tr>
<tr><td>11</td><td></td></tr>
<tr><td>12</td><td></td></tr>
<tr><td>13</td><td></td></tr>
<tr><td>14</td><td></td></tr>
<tr><td>15</td><td></td></tr>
<tr><td>16</td><td></td></tr>
<tr><td>17</td><td></td></tr>
<tr><td>18</td><td></td></tr>
<tr><td>19</td><td></td></tr>
<tr><td>20</td><td></td></tr>
</table>
</body>
</html>