[Parameter]
public EventCallback<PopupClosedEventArgs> Closed { get; set; }

<div @onclick="@(() => EulaVisible = true)">
    <p>CLICK TO SHOW A POP-UP WINDOW</p>
</div>

<DxPopup @bind-Visible="@EulaVisible"
         ShowFooter="true"
         HeaderText="DevExpress EULA"
         Closing="EulaPopupClosing"
         Closed="EulaPopupClosed">
    <BodyContentTemplate>
        <p>
            The terms of our license are fully outlined/described in the Developer Express Inc End User
            License Agreement (EULA) included with our product installations. Before you can install and use
            a Developer Express Inc product, you must read, understand and accept the terms/conditions of
            our EULAs. <a target="" _blank"" rel="" noopener noreferrer"" href=""
                          https: //www.devexpress.com/support/eulas/"">More info...</a>
        </p>
    </BodyContentTemplate>
    <FooterContentTemplate Context="Context">
        <DxCheckBox class="my-margin" @bind-Checked="@EulaAccepted">
            I accept the terms of the EULA
        </DxCheckBox>
        <DxButton RenderStyle="ButtonRenderStyle.Primary" Text="OK" Click="Context.CloseCallback" />
    </FooterContentTemplate>
</DxPopup>
@code {
    bool EulaAccepted { get; set; }
    bool EulaVisible { get; set; }

    void EulaPopupClosed(PopupClosedEventArgs args) {
        EulaAccepted = false;
    }
    void EulaPopupClosing(PopupClosingEventArgs args) {
        args.Cancel = !EulaAccepted;
    }
}

.my-margin {
    margin-left: 0; 
    margin-right: auto;
}

this.BodyContentTemplate = new RenderFragment<IPopupElementInfo>(target => BodyContent);
this.Closed = EventCallback.Factory.Create<PopupClosedEventArgs>(this, (e) => {
    OnClosed(e);