span.foo {
  background-color: navy;
  color: #bfd;
}

span.bar {
  background: rgba(105, 0, 12, 0.38);
  color: hsl(30, 100%, 50%);
  border-color: transparent;
}
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <title>Example</title>
    <style>
      a.not-a-class {
        color: red;
      }
    </style>
  </head>
  <body style="color:black"></body>
</html>