Generated by SassMeister.com.

BEM-addon.html

<div class="app-card">
  <div class="app-card--title"></div>
  <div class="app-card--content"></div>
</div>

<!-- a variation -->
<div class="app-card -tall">
  <div class="app-card--title"></div>
  <div class="app-card--content"></div>
</div>

y.sass

.app-card
  height: 400px
  
  &--title
    font-weight: bold
  
  &--content
    color: #ccc

/* a variation */
.app-card.-tall
  height: 800px
  
  .app-card--title
    font-size: 1.5em
  
  .app-card--content
    font-size: 1.1em

z.css

.app-card {
  height: 400px;
}
.app-card--title {
  font-weight: bold;
}
.app-card--content {
  color: #ccc;
}

/* a variation */
.app-card.-tall {
  height: 800px;
}
.app-card.-tall .app-card--title {
  font-size: 1.5em;
}
.app-card.-tall .app-card--content {
  font-size: 1.1em;
}