When an important rule is used on a style declaration, this declaration overrides any other declarations. Using !important, is bad practice and should be avoided because it makes debugging more difficult by breaking the natural cascading in your stylesheets.
Some rules of thumb
- Always look for a way to use specificity before even considering
!important
- Only use
!important on page-specific CSS that overrides foreign CSS (from external libraries, like Bootstrap or normalize.css).
- Never use
!important when you're writing a plugin/mashup.
- Never use
!important on site-wide CSS.