Vaadin theming is a nice way to reuse your Cascading Style Sheets across different projects. Vaadin 7 adds even more sugar to the whole theming thing since it allows you to use Syntactically Awesome Stylesheets.

The purpose of this article is not to describe technology since it's already well documented on the SASS website but to expose how to use SASS within Vaadin.

In order to use the SASS technology, a few steps are necessary:

• First, the UI base class has to be annotated with the @Theme annotation referencing our own new theme.

  @Theme("custom")
  public class SassUI extends UI {
      ...
  }

• Remember to set this UI as the Vaadin servlet parameter in the web deployment descriptor:

  <servlet>
      <servlet-name>VaadinServlet</servlet-name>
      <servlet-class>com.vaadin.server.VaadinServlet</servlet-class>
      <init-param>
          <param-name>UI</param-name>
          <param-value>com.morevaadin.vaadin7.sass.SassUI</param-value>
      </init-param>
  </servlet>

• Finally, instead of a CSS file, provide a styles.scss file under /VAADIN/themes/<name> (in your case, the name is "custom"). The code below is just an example:

  @import "../reindeer/styles.css";
   
  $color: rgb(51,204,255);
  $dark-color: darken($color, 20%);
  $spacing: 4px;
   
  .v-button-caption {
      color: $color;
  }
   
  @mixin border-radius($radius) {
      -webkit-border-radius: $radius;
      -moz-border-radius: $radius;
      border-radius: $radius;
  }
   
  .rounded-borders {
      @include border-radius(4px);
      border: 1px solid $color;
  }
   
  .v-label {
      color: $dark-color;
      padding-left: $spacing;
      margin-top: $spacing;
      margin-bottom: $spacing;
      font-weight: bold;
  }

Note that some SASS features are still missing at the time of this writing.

From http://morevaadin.com/content/vaadin-7-eases-your-theme-development