public Task ClosePopupAsync()

<DxScheduler StartDate="@DateTime.Today"
             DataStorage="@DataStorage"
             @ref="Scheduler">
    <Views>
        <DxSchedulerWeekView ShowWorkTimeOnly="false"
                             TimeIndicatorVisibility="SchedulerTimeIndicatorVisibility.Never"
                             TimeScale="@(new TimeSpan(0,15,0))"
                             WorkTime="@(new DxSchedulerTimeSpanRange(TimeSpan.FromHours(9), TimeSpan.FromHours(18)))"
                             VisibleTime="@(new DxSchedulerTimeSpanRange(TimeSpan.FromHours(8), TimeSpan.FromHours(19)))">
        </DxSchedulerWeekView>
    </Views>
    <AppointmentFormHeaderTemplate>
        <div class="popup-text-header">@context.Subject</div>
        <DxButton Click="@(() => Scheduler.ClosePopupAsync())"
                  Text="Close"
                  IconCssClass="btn-icon-close"
                  RenderStyle="ButtonRenderStyle.None"
                  CssClass="custom-button">
        </DxButton>
    </AppointmentFormHeaderTemplate>
</DxScheduler>

@code {
    ISchedulerAppointmentActions Scheduler { get; set; }

    DxSchedulerDataStorage DataStorage = new DxSchedulerDataStorage() {
        AppointmentsSource = AppointmentCollection.GetAppointments(),
        AppointmentMappings = new DxSchedulerAppointmentMappings() {
            Type = "AppointmentType",
            Start = "StartDate",
            End = "EndDate",
            Subject = "Caption",
            AllDay = "AllDay",
            Location = "Location",
            Description = "Description",
            LabelId = "Label",
            StatusId = "Status",
            RecurrenceInfo = "Recurrence"
        }
    };
}

.popup-text-header {
    margin-right: auto;
    text-overflow: ellipsis;
    overflow: hidden;
    white-space: nowrap;
}

.custom-button {
    color: white;
}

using System;

namespace Scheduler.Data
{
    public class Appointment {
        public Appointment() { }
        public int AppointmentType { get; set; }
        public DateTime StartDate { get; set; }
        public DateTime EndDate { get; set; }
        public string Caption { get; set; }
        public string Description { get; set; }
        public string Location { get; set; }
        public int? Label { get; set; }
        public int Status { get; set; }
        public bool AllDay { get; set; }
        public string Recurrence { get; set; }
        public int? ResourceId { get; set; }
        public bool Accepted { get; set; }
    }
}

using System;
using System.Collections.Generic;
using System.Globalization;

namespace Scheduler.Data
{
    public static partial class AppointmentCollection {
        public static List<Appointment> GetAppointments()
        {
            DateTime date = DateTime.Today;
            var dataSource = new List<Appointment>() {
               new Appointment {
                   Caption = "Upgrade Personal Computers",
                   StartDate = date + (new TimeSpan(0, 14, 0, 0)),
                   EndDate = date + (new TimeSpan(0, 16, 30, 0)),
                   Label = 1,
                   Status = 1
               },
               new Appointment {
                   Caption = "Install New Router in Dev Room",
                   StartDate = date + (new TimeSpan(0, 11, 30, 0)),
                   EndDate = date + (new TimeSpan(0, 13, 30, 0)),
                   Label = 6,
                   Status = 1
               },
               new Appointment {
                   Caption = "New Brochures",
                   StartDate = date + (new TimeSpan(1, 15, 00, 0)),
                   EndDate = date + (new TimeSpan(1, 16, 45, 0)),
                   Label = 8,
                   Status = 1
               },
               new Appointment {
                   Caption = "Approve Personal Computer Upgrade Plan",
                   StartDate = date + (new TimeSpan(3, 13, 30, 0)),
                   EndDate = date + (new TimeSpan(3, 16, 0, 0)),
                   Label = 1,
                   Status = 1
               },
               new Appointment {
                   Caption = "Customer Workshop",
                   StartDate = date + (new TimeSpan(4, 11, 0, 0)),
                   EndDate = date + (new TimeSpan(4, 12, 0, 0)),
                   AllDay = true,
                   Label = 8,
                   Status = 1
               },
               new Appointment {
                   Caption = "Upgrade Server Hardware",
                   StartDate = date + (new TimeSpan(6, 11, 0, 0)),
                   EndDate = date + (new TimeSpan(6, 13, 30, 0)),
                   Label = 6,
                   Status = 1
               },
               new Appointment {
                   AppointmentType = 1,
                   Caption = "Daily Meeting",
                   StartDate = date + (new TimeSpan(0, 9, 00, 0)),
                   EndDate = date + (new TimeSpan(0, 10, 00, 0)),
                   Label = 10,
                   Status = 1,
                   Recurrence = string.Format("<RecurrenceInfo Type=\"0\" Start=\"{0}\" Range=\"1\" OccurrenceCount=\"10\" Frequency =\"1\" Id=\"72e3db8f-cdb6-4aaa-afe1-e3c6b80ce995\"/>", ToString(date + (new TimeSpan(0, 9, 00, 0))))
               }
           };
            return dataSource;
        }

        private static string ToString(DateTime dateTime) {
            return dateTime.ToString(CultureInfo.InvariantCulture);
        }
    }
}