From the Silhoutte Blog...
I started by selecting the rounded square shape on the left-hand toolbar. The great thing about the rounded square is that you can use the right red toggle square to drag and create the "roundness" of your square or rectangle in this case.
I then resized it to fit the top a little better and overlapped it on the rectangle, I will end up welding it to the rectangle later. I did not make it the full width because here I am wanting to create a mat around the initial. In order to do this, select your text/initial and on the upper right-hand toolbar you will see the offset button. Click on it and then click on offset and drag the slider bar to the offset dimension you want to see. When you have it right where you want it, click apply. You can always resize your offset and font if it does fit on the rectangle like you want it.
Ok, now I want to add another little detail. I really like the bottom of the card shape: card_C20090727125838_19414. So I will import it from my library. Ungroup this shape so that the flourish design and the card are separate. You also want to group the flourish design to itself so that you don't loose all the little details. As you can see I rotated it to use its shape on the right side of the bookmark. Using the slice tool from the left-hand toolbar I start a little above the shape and drag it just a little below the shape. If you want to have a perfectly straight slice, hold the shift button while you drag the slice tool.