常用边框
border: solid 1px black
1像素的黑色边框
某一边的边框
border-top: solid 1px black
border-right: solid 1px black
border-bottom: solid 1px black
border-left: solid 1px black
上边框、右边框、下边框、做边框
透明边框
border: solid 1px rgba(206,35,35,0.1)
border: solid 1px rgba(206,35,35,0.4)
透明度0.1，透明度0.4
实线、虚线边框
border: solid 1px black
border: dashed 1px black
