Like state, modifiers also override styles. They are useful when modules (or components) have small and well understood differences.

Take an e-commerce site whereby each category has a unique background image in the header. All headers have the same padding, and margin etc. The only difference is the background image.

The boys category would have a modifier as follows:

<div class="categoryHeader categoryHeader--boys">

And similarly, the girls category would have a girls modifier:

<div class="categoryHeader categoryHeader--girls">

The CSS would be:

.categoryHeader {
  padding-top: 50px;
  padding-bottom: 50px;
  /* etc */

.categoryHeader--boys {
  background-image: url(/path/to/boys.jpg);

.categoryHeader--girls {
  background-image: url(/path/to/girls.jpg);

Because the differences are small and well understood, this type of reuse is more maintainable.

We can use the same approach for buttons. Most sites have a primary and secondary button style. If all that changes is one or two styles we can have a modifier for primary and secondary buttons as follows:

.button {
  padding: 20px;
  border-radius: 3px;
  /* etc */

.button--primary {
  background-color: green;

.button--secondary {
  background-color: #eee;

Again, this only works because the differences are well contained and well understood.

Final thought

Modifiers are a good way to reuse styles across a well understood element. But, the modifier itself should be a tweak. If it contains a lot of overrides, then modifiers are not the way to go. Instead use a module.


  1. Introduction
  2. Semantics
  3. Reuse
  4. IDs
  5. Conventions
  6. Modules
  7. State
  8. Modifiers
  9. Versioning
  10. Javascript
  11. Organisation
  12. FAQs

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