valo: content-property value should be normal or none

Hi all,

The valo theme uses the content property in many xxx:after rules with an empty string as its value. This is not equivalent to:

content: normal;   /* this is the default */

or to:

conten: none;      /* 'normal' evaluates to 'none' */

as can be seen within the following example.
Java:

@SuppressWarnings("serial")
@Theme("test")
public class TestUI extends UI {

    private static final String CLICK_ME = "Click me";

    @WebServlet(value = "/*", asyncSupported = true)
    @VaadinServletConfiguration(productionMode = false, ui = TestUI.class)
    public static class Servlet extends VaadinServlet {
    }

    @Override
    protected void init(VaadinRequest request) {
        VerticalLayout layout = new VerticalLayout();
        layout.setMargin(true);
        Button button = new Button(CLICK_ME);
        layout.addComponent(button);
        setContent(layout);
    }

SCSS:

$v-font-weight:                   300;
$v-font-size:                     13px;
$v-font-family:                   Arial, Helvetica, sans-serif;

@import "../valo/valo.scss";

@mixin test {
  @include valo;

  $lighter:                       #E1FBE1;
  $dark:                          #506450;
  $darkest:                       #225522;
  $button-color:                  #FFFF00;
  $button-border-color:           #FF0000;

  // Insert your own theme rules here
  .v-ui {
    background-color:            $lighter;
    font:                        $v-font-weight $v-font-size $v-font-family;
  }
 
  .v-button {
    background-image:            none;
    box-shadow:                  none;
    background-color:            $dark;
    color:                       $button-color;
    width:                       8em;
    
    &:focus {
      &, &:after {
        position:                inherit;
        background-color:        $darkest;
        color:                   $button-color;
        border:                  3px solid $button-border-color;
      }
    }
  }
}

If the button gets the focus (using the tab key), the button caption is extended by an ugly, border-colored part (tested with FF v43.0.1 and IE v11.0.28). See the following image:

Hence the property value should be changed to:

content: normal;

Thanks el goog