Add more validation to CSSProperties

[suryarajendhran]

The CSS values that are passed to modify the CSS property should be valid, else the properties will not be overridden. So adding validation should help.

(Although this might be partly solved by checking whether the properties are actually modified after the fact but that is not the most accurate way to check if an invalid CSS value was provided. CSS properties could be overridden by other higher precedence property/rule or in cases where the CSS is dynamically manipulated.)

For example, the following function will fail to actually modify the CSS rule but no errors will be thrown.

import { modifyCSSRule } from 'change-css';

modifyCSSRule('body', {
  color: '#01g'
});