It's just so darn easy to make a coordinating envelope liner. I recommend not using cardstock, but cheap copy paper. Easier to bend. And cheaper.
In this case, after making the polka dots with some of the circles in the Hero Arts Flower Dauber set, I hand drew some lines on the one layer card. And then on the copy paper for the envelope. (Sentiment by Avery Elle)
Stripes and lines are a good combo and, by using the same markers to color both the dots and the stripes, I got a nice cohesive design. Not very risky, but I'm a bit rusty!
By the way, the dots carry over to the back of the card.
MOOD WHEN DONE = Colorful