Defines the maximum height the element can be.
默认属性
max-height: none;
The element has no limit in terms of height.
max-height: 2000px;
You can use numeric values like pixels, (r)em, percentages...
If the maximum height is larger than the element's actual height, the max height has no effect.
max-height: 100px;
If the content does not fit within the maximum height, it will overflow. How the container will handle this overflowing content is defined by the overflow property.