3. Thou shalt not use ID selectors, even if thou thinkest thou hast to

The limitations of IDs in a complex UI are well documented. In summary, they are far more specific than a class selector - therefore making overrides more difficult. Plus they can only be used once in the page anyway so their efficacy is limited.

Tip

Remember we dealt with specificity in detail back in Chapter 2, The Problems of CSS at Scale.

With ECSS we do not use ID selectors in the CSS. They present no advantages over class based selectors and introduce unwanted problems.

In the almost unbelievable situation where you HAVE to use an ID to select an element, use it within an attribute selector instead to keep specificity lower:

[id="Thing"] {
    /* Property/Values Here */
}