比如我用代码在窗体上建立了这样的10个控件
int top=0,left=20;
 for (int i = 0; i < 10; i++)
 {               
         Button btn = new Button();
         btn.Width = 110;
         btn.Height = 50;
         btn.Left =left;
         btn.Top = top;
         left += 120;
         if (((i +1)% 5) == 0)
           {
                    top += 60;
                    left =20;
                }
}
我现在想把第1行的第三个控键背景改成蓝色```
应该怎么写呢……