설명
/* Block component */
.btn {}
/* Element that depends upon the block */
.btn__price {}
/* Modifier that changes the style of the block */
.btn--orange {}
.btn--big {}사용 예시
<a class="btn btn--big btn--orange" href="https://css-tricks.com">
<span class="btn__price">$9.99</span>
<span class="btn__text">Subscribe</span>
</a>
:)