Vaadin 7 - SCSS - Import Custom CSS

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:

 1 @import "../reindeer/styles.css";
 2 @import "../YOUR_CUSTOM_STYLES.css";

 3 $color: rgb(51,204,255);
 4 $dark-color: darken($color, 20%);
 5 $spacing: 4px;
 6  
 7 .v-button-caption {
 8     color: $color;
 9 }
10  

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