#background-clip
Defines how far the background should extend within the element.
默认属性
background-clip: border-box;
The background extends completely throughout the element, even under the border.
background-clip: padding-box;
The background only extends to the edge of the border: it includes the padding but not the border.
background-clip: content-box;
The background only extends to the edge of the content: it doesn't include the padding, nor the border.