button1.FlatStyle = FlatStyle.Flat;//style
button1.ForeColor = Color.Transparent;//前景
button1.BackColor = Color.Transparent;//去背景
button1.FlatAppearance.BorderSize = 0;//去边线
//button1.FlatAppearance.MouseOverBackColor = Color.Transparent;//鼠标经过
//button1.FlatAppearance.MouseDownBackColor = Color.Transparent;//鼠标按下