How to apply Watermark to TatxBox and iCheck plugin to CheckBox using jQuery in ASP.Net

Hi nedash,

Please refer the below code and modify as per your requirement.

HTML

<form id="form1" runat="server">
<div>
    <asp:CheckBox ID="CheckBox1" Text="text" runat="server" />
    <br />
    <asp:TextBox ID="Txtage" Text="جستجو بر اساس کد ملک" onblur="WaterMark(this, event,'جستجو بر اساس کد ملک');"
        runat="server" class="txtser" onfocus="WaterMark(this, event,'جستجو بر اساس کد ملک');" />
    <br />
    <asp:ScriptManager ID="ScriptManager1" runat="server" />
    <asp:UpdatePanel ID="UpdatePanel1" runat="server">
        <ContentTemplate>
            <asp:DropDownList ID="DropDownList1" CssClass="dropdownlist" runat="server">
                <asp:ListItem Text="text1" />
                <asp:ListItem Text="text2" />
                <asp:ListItem Text="text3" />
                <asp:ListItem Text="text4" />
                <asp:ListItem Text="text5" />
                <asp:ListItem Text="text6" />
            </asp:DropDownList>
        </ContentTemplate>
    </asp:UpdatePanel>
</div>
<div>
    <script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
    <link href="red.css" rel="stylesheet" type="text/css" />
    <script src="icheck.js"></script>
    <script src="jquery.selectric.js" type="text/javascript"></script>
    <link href="selectric.css" rel="stylesheet" type="text/css" />
    <script type="text/javascript">
        window.onload = function SetColorOnPageLoad() {
            var defalutage = "مثال: 12 سال";
            functionSetColor(document.getElementById("Txtage"), defalutage);
            ApplyCss();
        }

        function functionSetColor(Textbox, WaterMark) {

            if (Textbox.value.length > 0 && Textbox.value == WaterMark) {
                Textbox.style.color = "#443f13";
                Textbox.style.fontSize = "14.5px";

            }
            else {
                Textbox.style.color = "white";
                Textbox.style.fontSize = "14.5px";
            }
        }

        function WaterMark(txt, evt, msg) {

            if (txt.value.length == 0 && evt.type == "blur") {
                txt.style.color = "#443f13";
                txt.value = msg;
                txt.style.fontSize = "14.5px";
                txt.style.fontfamily = "behtop_Yekan";
            }

            if (txt.value == msg && evt.type == "focus") {
                   
                txt.style.color = "white";
                txt.value = "";
                if (txt.name == "Txtage") {
                    txt.style.fontSize = "25px";
                }
                else {
                    txt.style.fontSize = "14.5px";
                }
                txt.style.fontfamily = "behtop_Yekan";
            }
        }

        function ApplyCss() {
            $('select').selectric({
                maxHeight: 200
            });

            $('input[type=Checkbox]').iCheck({
                checkboxClass: 'icheckbox_square-red',
                increaseArea: '20%'
            });
        }

        var prm = Sys.WebForms.PageRequestManager.getInstance();
        if (prm != null) {
            prm.add_endRequest(function (sender, e) {
                if (sender._postBackSettings.panelsToUpdate != null) {
                    ApplyCss();
                }
            });
        };

    </script>
</div>
<div>
    <style type="text/css">
        .txtser
        {
            font-size: 25px;
            width: 150px;
            height: 25px;
            margin: 23px 38px 0 0;
            background-color: #000;
            border: 1px solid #000;
            color: #fff;
            font-family: m1;
            text-align: center;
        }
    </style>
</div>
</form>

Screenshot