How to combine class and ID in CSS selector?

If I have the following div:

<div class="sectionA" id="content">
    Lorem Ipsum...
</div>

Is there a way to define a style that expresses the idea “A div with id='content' AND class="myClass"“?

Or do you have simply go one way or the other as in

<div class="content-sectionA">
    Lorem Ipsum...
</div>

Or

<div id="content-sectionA">
    Lorem Ipsum...
</div>