What controller even to use?

I am using a ComboBox and a Panel. What I want to do is when I click on the ComboBox, the Panel would appear.

The problem is, I want to still be able to activate a CheckBox inside the Panel but the ComboBox and Panel would be close together once I lose focus.

Is there a possible way to do this?

My temporary solution is this:

---

panelCol.MouseLeave += (s, e) =>
{
  panelCol.Visible = false;
};

tp.Click += (s, e) =>  //tp is a tabPage.
{
  panelCol.Visible = false;
};

dataGridView.Click += (s, e) =>
{
  panelCol.Visible = false;
};

---