Edit in JSFiddle

$(function () {
    $("#b1").click(function () {
        $("#div1").css("border", "solid black 1pt");
    });
    $("#b2").click(function () {
        $(".c2").css("backgroundColor", "blue");
    });
    $("#b3").click(function () {
        $("p").css("backgroundColor", "yellow");
    });
});

<div>
    <input id="b1" type="button" value="#id" />
    <input id="b2" type="button" value=".C" />
    <input id="b3" type="button" value="E" />
</div>
<div id="div1" class="c1">
    <p>p1-1</p>
    <p>p1-2</p>
    <p>p1-3</p>
</div>
<div id="div2" class="c2">
    <p>p2-1</p>
    <p>p2-2</p>
    <p>p2-3</p>
</div>
<div id="div3" class="c3">
    <p>p3-1</p>
    <p>p3-2</p>
    <p>p3-3</p>
</div>