As mentioned, I added a background on the sleeve/envelope part of my secret slider thank you note. The burst actually comes from the circus invitation, though I've tweaked the colors. The tiger comes from that card as well.
I really like how this is coming along.
One thing I'm wanting to tweak, though. The window flap doesn't quite lie flat because it's been "trained" to flip up. Consequently, in its resting state, there's a tiny gap at the bottom of it where it doesn't quite close up, unless you hold it shut.