private void btnEntrance_Click(object sender, EventArgs e)
{
var entranceMain = new frmEntrance();
entranceMain.Show();
}
private void entranceMenuItem_Click(object sender, EventArgs e)
{
this.pnlMain.Controls.Clear();
var entranceForm = new frmEntrance { TopLevel = false, AutoScroll = true, Dock = DockStyle.Fill };
pnlMain.Controls.Add(entranceForm);
entranceForm.Show();
}