List item span all the way

Here we have a list. It's not as straight forward as it seems to make the active list item be selected all the way to the left,

The trick is to use a pseudo element that spans all the way out.

HTML

<div class="menu">
  <ul>
    <li>
      <a href="#">Level 1</a>
      <ul>
        <li class="active">
          <a href="#">Level 2</a>
        </li>
      </ul>
    </li>
    <li><a href="#">Level 1</a></li>
  </ul>
</div>

CSS

.menu {
  background: #eee;
  width: 200px;
  overflow: hidden;
}

.menu > ul > li {
  padding: 0;
}

.menu ul {
  list-style: none;
  margin: 0;
  padding: 0;
}

.menu li {
  padding-left: 2rem;
  position: relative;
}

.menu li.active:before {
  content: "";
  position: absolute;
  top: 0;
  bottom: 0;
  right: 0;
  left: -100vw;
  background: #000;
  z-index: 0;
}

.menu li.active a {
  color: #fff;
}

.menu a {
  display: block;
  position: relative;
  z-index: 1;
  padding: .5rem;
}

Sources

• https://stackoverflow.com/a/48706072/148496