bem css

1/* Block component */
2.btn {}
3
4/* Element that depends upon the block */ 
5.btn__price {}
6
7/* Modifier that changes the style of the block */
8.btn--orange {} 
9.btn--big {}

1.form { }
2.form--theme-xmas { }
3.form--simple { }
4.form__input { }
5.form__submit { }
6.form__submit--disabled { }