Since :before is a pseudo element, you can't have html content, only text.
Chemical industry, complex of processes, operations, and organizations engaged in the manufacture of chemicals and their derivatives. Raw materials include fossil fuels and inorganic chemicals. An average chemical product is passed from factory to factory several times before it emerges into the market.
Chemical Banking Corporation, former American bank holding company that merged with The Chase Manhattan Corporation in 1996. The holding company’s principal subsidiary was Chemical Bank, which was chartered in 1824 in New York City as a division of the New York Chemical Manufacturing Company.
An equation is any expression with an equals sign, so your example is by definition an equation. Equations appear frequently in mathematics because mathematicians love to use equal signs. A formula is a set of instructions for creating a desired result. Non-mathematical examples include such things as chemical formulas (two H and one O make H2O), or the formula for Coca-Cola (which is just a ...
If we want an equation $f (x, y)$ for the line, the domain of $f$ can only be the shadow of the line on the $xy$ plane. But any nice function $f$ will have as a domain either all pairs $ (x, y)$, or almost all of them.
The ::before notation (with two colons) was introduced in CSS3 in order to establish a discrimination between pseudo-classes and pseudo-elements. Browsers also accept the notation :before introduced in CSS 2.
So I read the docs and probably understand the purpose of ::before and ::after. If my understanding is correct, they should always work in combination with other elements. But the web page I'm look...