private void categoryButton_Click(object sender, EventArgs e)
{
activePanel.Height = categoryButton.Height;
activePanel.Top = categoryButton.Top;
CategoryUiController categoryUiController = new CategoryUiController();
mainPanel.Controls.Clear();
categoryUiController.Dock = DockStyle.Fill;
categoryUiController.BringToFront();
categoryUiController.Focus();
mainPanel.Controls.Add(categoryUiController);
}