I am trying to create custom css classes for my Wordpress

I am trying to create custom css classes for my Wordpress site, but it's not working.
http://tinyurl.com/lwey2ex

I have the following in my css style sheet:

.big-text {font-size: 20px; color: #454545}
.big-blue-text {font-size: 20px; color: #5A92A5}

... and this in the text editor area:
<span class="big-text">Excepteur sint occaecat </span>cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id er.

<span class="big-blue-text">Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum. </span>

Am I doing something wrong?