Change CSS Element That Comes After Another

I would like to hover in a.bio change the background .pic to green. I tried some ways, but it did not work out. I did not understand the logic of ~ and how even to make it work.

Solution 1:

Move your a.bio in your HTML, because ~ is a sibling selector (however less strict than the +), and use position to stay as it was before moving the HTML:

Snippet

.executivo .pic::after {
  background-color: #00845b;
  content: "";
  height: 100%;
  left: 0;
  position: absolute;
  top: 0;
  width: 100%;
  opacity: 0;
  transition: .3s ease-in-out;
}
.executivo {
  position: relative;
}
.executivo a.bio {
  position: absolute;
  bottom: -20px
}
.executivo a.bio:hover ~ .pic img {
  opacity: 0.35;
}
.executivo .pic {
  margin-bottom: 45px;
  position: relative;
}
.executivo .pic img {
  display: block;
  max-width:100% /*demo*/
}

<div class="executivo">
  <a class="bio" href="#">Bio+</a>
  <div class="pic">
    <img src="//lorempixel.com/1600/900" alt="alt text" />
  </div>
  <div class="title">
    <h3>title</h3>
  </div>
</div>

Solution 2:

Nex element selector is

+

And direct decedent is

>

in css.

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