Listbox problem change font C# WFA or add image to listbox which contains same text in textbox and listbox?

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C#

Hello

I have one textbox, one button and one listbox... I want to do this: When i add some text into textbox, and that text is allrady existing in listbox, a want to change font and bold that item in listbox... Can someone help me????

Or this: I want to add green dot to text in listbox which are matching in textbox???

private void button1_Click(object sender, EventArgs e)
    { 
    if (listBox1.Items.Contains(textBox1.Text) == false)
    {
        listBox1.Items.Add(textBox1.Text);
    }
    else
    {
        MessageBox.Show("It's allrady in listbox");
        //need to change font and bold that item in listbox
        //or add green dot to text in listbox
    }
}