GTKD - CSS class color "flash" delay

[TheDGuy via Digitalmars-d-learn]

Hello,

i would like to flash some buttons with CSS. My current approach:

         for(int i = 0; i < level; i++){
             Button currentButton = bArr[rndButtonBlink[i]];
             ListG list = 
currentButton.getStyleContext().listClasses();
             string CSSClassName = 
to!string(cast(char*)list.next().data);
             currentButton.getStyleContext().addClass(CSSClassName 
~ "-flash");
             writeln(CSSClassName);
             //some kind of delay
             
currentButton.getStyleContext().removeClass(CSSClassName ~ 
"-flash");
         }

The color changing part works fine but if i use some kind of 
delay the program just starts delayed but no color changing 
happens. I am wondering why, because everything is executed in 
one thread, so the execution order looks like this to me:

1. Start GUI
2. Change Button Color to flash color
3. Wait 2 sec
4. Change Button Color back to standard

but instead it looks like this:

1. Wait 2 sec
2. Start GUI
3. Change Button Color to flash color
4. Change Button Color back to standard

Now because a delay is missing the change between the colors 
happens unnoticeable fast.

I hope i can get around it without getting into multithreading?