如何重新打开纯CSS3模态对话框

我有以下模态对话框(弹出)使用只有CSS3在我的asp页面的用户注册:HTML:

<%-- Modal PopUp starts here--%>
<div id="openModal" class="modalDialog">
    <div>   <a href="#close" title="Close" class="close" onclick="DisableAllPopUpTxt()">X</a>
        <table style="width:100%;">
            <tr>
                <td style="text-align: center; width: 100%;"></td>
            </tr>
            <tr>
                <td style="text-align: center; width: 100%;">
                    <asp:Label ID="lblErrorMSG2" runat="server" Font-Bold="True" ForeColor="#FF3300" Text="Email ID Already Taken " Visible="False"></asp:Label>
                </td>
            </tr>
            <tr>
                <td style="text-align: center; width: 100%;">
                    <input id="txtCustFName" name="txtCustFName" type="text" required placeholder="Enter Your First Name" style="width: 80%" />
                </td>
                </td>
            </tr>
            <tr>
                <td style="text-align: center; width: 100%;">
                    <input id="txtCustLName" name="txtCustLName" type="text" required placeholder="Enter Your Last Name" style="width: 80%" />
                </td>
                </td>
            </tr>
            <tr>
                <td style="text-align: center; width: 100%;">
                    <input id="txtCustREmail" name="txtCustREmail" type="email" required placeholder="Enter Valid Email ID" style="width: 80%" />
                </td>
                </td>
            </tr>
            <tr>
                <td style="text-align: center; width: 100%;">
                    <input id="txtCustRPwd" name="txtCustRPwd" type="password" required placeholder="Enter Password" style="width: 80%" />
                </td>
                </td>
            </tr>
            <tr>
                <td style="text-align: center; width: 100%;">
                    <input id="txtCustRePwd" name="txtCustRePwd" type="password" required placeholder="ReType Password" style="width: 80%" />
                </td>
                </td>
            </tr>
            <tr>
                <td style="text-align: center; width: 100%;">
                    <input id="txtCustPh" name="txtCustPh" type="number" size="10" min="10" max="10" required placeholder="Enter Valid Mobile No" style="width: 80%" />
                </td>
                </td>
            </tr>
            <tr>
                <td class="style1" style="text-align: center; width: 100%;" onclick="btnSignUp()">
                    <asp:Button ID="btnSingUp" runat="server" onclick="signUp" Text="Login" />
                </td>
            </tr>
            <tr>
                <td style="text-align: center; width: 100%;"> </td>
            </tr>
        </table>
    </div>
</div>
<%--Modal PopUp Ends Here--%>

CSS:

.modalDialog {
    position: fixed;
    font-family: Arial, Helvetica, sans-serif;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    background: rgba(0,0,0,0.8);
    z-index: 99999;
    opacity:0;
    -webkit-transition: opacity 400ms ease-in;
    -moz-transition: opacity 400ms ease-in;
    transition: opacity 400ms ease-in;
    pointer-events: none;
    }
.modalDialog:target {
    opacity:1;
    pointer-events: auto;
    }
.modalDialog > div {
    width: 400px;
    position: relative;
    margin: 10% auto;
    padding: 5px 20px 13px 20px;
    border-radius: 10px;
    background: #fff;
    background: -moz-linear-gradient(#fff, #999);
    background: -webkit-linear-gradient(#fff, #999);
    background: -o-linear-gradient(#fff, #999);
    }
.close {
    background: #606061;
    color: #FFFFFF;
    line-height: 25px;
    position: absolute;
    right: -12px;
    text-align: center;
    top: -10px;
    width: 24px;
    text-decoration: none;
    font-weight: bold;
    -webkit-border-radius: 12px;
    -moz-border-radius: 12px;
    border-radius: 12px;
    -moz-box-shadow: 1px 1px 3px #000;
    -webkit-box-shadow: 1px 1px 3px #000;
    box-shadow: 1px 1px 3px #000;}
.close:hover { background: #00d9ff; 
               }

在我的asp页面中，我遵循锚标记，用于显示弹出窗口:

现在问题是:

因为这是注册表单，我想现有的电子邮件id的服务器端验证。如果用户输入的email id已经在数据库中存在，我想重新打开上面的模态对话框，并提示email id已经存在。

我无法重新打开该对话框。是否有任何方法来做到这一点使用js?请帮帮我。

模态对话框的教程在网站上:点击这里

用于显示模态对话框:点击这里

.modalDialog:target, .modalDialog.target {
  opacity:1;
  pointer-events: auto;
}

$('.modalDialog').addClass('target')