Am I subclassing my CSS correctly?

Question

I am making a set of buttons for my site, and I am in need of some professional insight.

In order to reduce CSS bloat, I want to subclass my buttons for different colors, ex .button.blue .

Will the following incur issues in the future? (assuming I don't make a class of just .blue) Do I have to use something like .button.button-blue instead?

.button {
  display:inline-block;
  padding: 9px 18px;
  margin: 20px;
  text-decoration: none;
  font-family: Arial, Helvetica, sans-serif;
  font-size: 12px;
  font-weight: bold;
  text-align: center;
  background: #FFE150;
}
.button.blue {
  background: #49b8e7;
  border:1px solid #54abcf;
  border-bottom:1px solid #398fb4;
  color:#FFF
  text-shadow: 0 1px 0 rgba(255,255,255, 0.5);
}
.header{
  height: 50px;
}
.header.blue {
  background: blue;
  color: #fff;
}

Answer 1

What you have there with the multi-classes will work fine assuming you want them to work like so:

<div class="button blue">
Will use .button and .button.blue
</div>

<div class="button">
Will only use .button
</div>

<div class="header blue">
Will  use .header and .header.blue
</div>

<div class="header">
Will only use .header
</div>

<div class="blue">
Will use neither of the .blue declarations because it doesn't contain header or button.
</div>

Answer 2

A selector like .button.blue actually selects for an element with that has both "blue" and "button" as classes, not a class called .button.blue. See http://www.w3.org/TR/CSS21/selector.html#class-html.

You can use the .button.blue style rule you have listed, but you'll need to rearrange your HTML so that you have something like <button type="button" class="button blue"/>. However, you don't really need to have a button class since it being a button (or <input type="submit">, etc.) is enough to use in your selector. You could write a CSS rule that is simply button.blue, input[type=submit].blue{}