Defines the minimum height of the element.
默认属性
min-height: 0;
The element has no minimum height.
min-height: 200px;
You can use numeric values like pixels, (r)em, percentages...
If the minimum height is larger than the element's actual height, the min height will be applied.
min-height: 5px;
If the minimum height is smaller than the element's actual height, the min height has no effect.