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$(function () {
    $("#btn1").click(function () {
        $("table td:first-child").css("backgroundColor", "red");
    });
            
    $("#btn2").click(function () {
        $("table td:last-child").css("backgroundColor", "yellow");
    });

    $("#btn3").click(function () {
        $("table td:nth-child(3n+2)").css("backgroundColor", "blue");
    });

    $("#btn4").click(function () {
        $("table td:nth-last-child(3n+2)").css("backgroundColor", "gray");
    });
});

<div>
    <input id="btn1" type="button" value=":first-child" />
    <input id="btn2" type="button" value=":last-child" />
    <input id="btn3" type="button" value=":nth-child" />
    <input id="btn4" type="button" value=":nth-last-child" />
</div>
<table border="1">
    <tr>
        <td>01</td>
        <td>02</td>
        <td>03</td>
        <td>04</td>
        <td>05</td>
        <td>06</td>
        <td>07</td>
        <td>08</td>
        <td>09</td>
        <td>10</td>
    </tr>
    <tr>
        <td>11</td>
        <td>12</td>
        <td>13</td>
        <td>14</td>
        <td>15</td>
        <td>16</td>
        <td>17</td>
        <td>18</td>
        <td>19</td>
        <td>20</td>
    </tr>
    <tr>
        <td>21</td>
        <td>22</td>
        <td>23</td>
        <td>24</td>
        <td>25</td>
        <td>26</td>
        <td>27</td>
        <td>28</td>
        <td>29</td>
        <td>30</td>
    </tr>
</table>