width property
宽。如果只有 width,而没有 height,将获得一个水平方向的虚线 如果同时有 width 和 height,将获得一个虚线边框。
width. If there is only width and no height, you will get a dotted line in the horizontal direction If there are both width and height, you will get a dotted border.
Implementation
final double? width;