You use both (without space between them)
.checked.featured{
// ...
}
Reference: http://www.w3.org/TR/selectors/#class-html
Example
div{margin:1em;padding:1em;}
.checked{color:green;}
.featured{border:1px solid #ddd;}
.checked.featured{
font-weight:bold;
}
<div class="checked">element with checked class</div>
<div class="featured">element with featured class</div>
<div class="featured checked">element with both checked and featured classes</div>