The mind must be given relaxation; it will arise better and keener after resting. As rich fields must not be forced-for their productiveness, the have no rest, will quickly exhaust them constantlabor will break the vigor of the mind, but if it is released and relaxed a little while, it will recover its powers
Seneca

<percentage>

The <percentage> CSS data type represents a percentage value. It is often used to define a size as relative to an element's parent object. Numerous properties can use percentages, such as width, height, margin, padding, and font-size.
<percentage> css reference