JavaScript why cannot select the elements

I’m sure I’ve make a mistake but I can’t figure it out…

Why I cannot select the elements with class name test by `querySelectorAll?

I’m getting an error: cannot read properties of undefined, but the elements are definitely defined because when I type content in the console, it shows the nodeList…

const content = document.querySelectorAll('.test');

content.classList.add('hide-content');

.Content {
  width: 180px;
  height: 90px;
  background-color: green;
}

.hide-content {
  display: none
}

<div class="Content"></div>
<div class="Content test"></div>
<div class="Content test"></div>