[CSS] & [JQUERY] [selettore] :first-child

Esempi

<table>
  <tr><td>1</td><td>2</td><td>3</td></tr>
  <tr><td>4</td><td>5</td><td>6</td></tr>
  <tr><td>7</td><td>8</td><td>9</td></tr>
  <tr><td>10</td><td>11</td><td>12</td></tr>
  <tr><td>13</td><td>14</td><td>15</td></tr>
</table>
<style>
tr:first-child {
  background-color: yellow;
}
</style>

<style>
ol > :first-child {
    background-color:yellow;
}
</style>
<ol>
  <li>a</li>
  <li>b</li>
  <li>c</li>
</ol>
<ol>
  <li>d</li>
  <li>e</li>
  <li>f</li>
</ol>