How to set/change/remove focus style on a Button in C#?

Is this the effect you are looking for?

public class NoFocusCueButton : Button
{
    protected override bool ShowFocusCues
    {
        get
        {
            return false;
        }
    }
}

You can use this custom button class just like a regular button, but it won't give you an extra rectangle on focus.

I had the same issue with the annoying double border, and stumbled across this thread looking for an answer...

The way I solved this was to set the BorderSize to 0 then draw my own border in OnPaint

*Note: Not the entire button, just the border

A simple example would be:

public class CustomButton : Button
{
    public CustomButton()
        : base()
    {
        // Prevent the button from drawing its own border
        FlatAppearance.BorderSize = 0;
        FlatStyle = System.Windows.Forms.FlatStyle.Flat;
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        base.OnPaint(e);

        // Draw Border using color specified in Flat Appearance
        Pen pen = new Pen(FlatAppearance.BorderColor, 1);
        Rectangle rectangle = new Rectangle(0, 0, Size.Width - 1, Size.Height - 1);
        e.Graphics.DrawRectangle(pen, rectangle);
    }
}

In my case, this is how I made a button that mimics a ToolStripButton, where the border is only visible when you hover over the button:

public class ToolButton : Button
{
    private bool ShowBorder { get; set; }

    public ToolButton()
        : base()
    {
        // Prevent the button from drawing its own border
        FlatAppearance.BorderSize = 0;

        // Set up a blue border and back colors for the button
        FlatAppearance.BorderColor = Color.FromArgb(51, 153, 255);
        FlatAppearance.CheckedBackColor = Color.FromArgb(153, 204, 255);
        FlatAppearance.MouseDownBackColor = Color.FromArgb(153, 204, 255);
        FlatAppearance.MouseOverBackColor = Color.FromArgb(194, 224, 255);
        FlatStyle = System.Windows.Forms.FlatStyle.Flat;

        // Set the size for the button to be the same as a ToolStripButton
        Size = new System.Drawing.Size(23, 22);
    }

    protected override void OnMouseEnter(EventArgs e)
    {
        base.OnMouseEnter(e);

        // Show the border when you hover over the button
        ShowBorder = true;
    }

    protected override void OnMouseLeave(EventArgs e)
    {
        base.OnMouseLeave(e);

        // Hide the border when you leave the button
        ShowBorder = false;
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        base.OnPaint(e);

        // The DesignMode check here causes the border to always draw in the Designer
        // This makes it easier to place your button
        if (DesignMode || ShowBorder)
        {
            Pen pen = new Pen(FlatAppearance.BorderColor, 1);
            Rectangle rectangle = new Rectangle(0, 0, Size.Width - 1, Size.Height - 1);
            e.Graphics.DrawRectangle(pen, rectangle);
        }
    }



    // Prevent Text from being set on the button (since it will be an icon)
    [Browsable(false)]
    public override string Text { get { return ""; } set { base.Text = ""; } }

    [Browsable(false)]
    public override ContentAlignment TextAlign { get { return base.TextAlign; } set { base.TextAlign = value; } }
}

Make a custom button:

public partial class CustomButton: Button
{
    public ButtonPageButton()
    {
        InitializeComponent();

        this.SetStyle(ControlStyles.Selectable, false);
    }
}

That'll get rid of that annoying border! ;-)