Even though I'm one of the last people who should be replying to this thread (
here's why), I can answer the 3D question. The simple way to make a rectangle stand out is to add a few pixels to the right and bottom edges, outside the normal border, with a color that represents a shadow.
You could use any color darker than the border color, or use the same color as the border with the saturation value changed, or use a shade of gray.
Optionally, you can a border of the same small width to the top and left, with a light shade, but that's not as important as the bottom right.
It fools us into thinking it is 3D because we are used to objects in 3D casting shadows below objects. Whether the shadow falls to the right or left is less important.
In any image editor, the process is to increase the size of the image by a few pixels to fit the new borders and then fill the areas on those sides with the colors you have chosen. If you are using only 2 new borders (not 4), you can use the paint can tool to fill the new area with the color you chose. If you have 4 border areas, you can select each border area as a rectangle and fill the selection area with the color you chose.