Generated by SassMeister.com.

SassMeister-input-HTML.html

<div class="header  header--sticky">
  <div class="header__container  header__container--active">
    <nav>navigation</nav>
  </div>
</div>

SassMeister-input.scss

// ----
// libsass (v3.2.5)
// ----

.header {
  display: block;
  width: 100%;
  padding: 1em;
  background: blue;
  
  &__container {
    padding: 1em;
    background: orange;
    
    &--active {
      background: red;
    }
  }
  
  &--sticky {
    position: fixed;
    top: 0;
    left: 0;
  }
}

SassMeister-output.css

.header {
  display: block;
  width: 100%;
  padding: 1em;
  background: blue;
}

.header__container {
  padding: 1em;
  background: orange;
}

.header__container--active {
  background: red;
}

.header--sticky {
  position: fixed;
  top: 0;
  left: 0;
}

SassMeister-rendered.html

<div class="header  header--sticky">
  <div class="header__container  header__container--active">
    <nav>navigation</nav>
  </div>
</div>