Add class from application.css to email message

Hello.

I've added in the application.css my style:

.plus {
  font-size: 15pt;
  font-weight: bold;
  color: green;
  text-indent: 20px;
  background: url(images/plus.png) no-repeat 0;
}

Now, i can write in issues description:

p(plus). Example

And its work. But on email come html with code:

<p class="plus">Example</p>

And there is no '.plus' in style section.
How to add a css class in message?

Redmine