What is the W3C?
The World Wide Web Consortium (W3C), is an international community where its members work together to implement web standards that can be used without the need to implement proprietary code in every browser.
W3C promotes the use of standards to minimize the effort in developing digital pages or platforms and can be accessible to anyone (even if you have some limitation). In other words, W3C wants the web to be used and accessible to everyone.
All modern browsers implement web standards correctly, but in the older versions certain fixes have to be applied so that a page can be seen properly to the web design that has been done.
Developers must also take into account that when converting a design (PSD, Sketch, Figma, Zeplin, etc.) to HTML, the markup tags established by the W3C must be used correctly. Just as HTML has standards, CSS also has parameters that must be respected so that it can be accessible to anyone.
So you know if you are a front-end developer or a layout designer, you must know the rules of web standards so you do not have errors in your coding.