<length-percentage>

The <length-percentage> CSS data type represents a value that can be either a length or a percentage.
The <length-percentage> CSS数据类型表示一个值，该值可以是<length>或<percentage>。

Refer to the documentation for length and percentage for details of the individual syntaxes allowed by this type.

Where a <length-percentage> is specified as an allowable type, this means that the percentage resolves to a length and therefore can be used in a calc() expression. Therefore, all of the following values are acceptable for width:

width: 200px;
width: 20%;
width: calc(100% - 200px);