Now we need to mask the group so that any shading we apply stays within the borders of the shape. Select the background shape again and go Cmd/Ctrl + C > Cmd/Ctrl + F > Cmd/Ctrl + Shift + ] to copy it and paste in the same place, then bring the copy to the front. Click the Make/Release Clipping Mask button in the bottom left of the Layers palette to mask the group.
Now we need to add the shading around the edges of the shape. Select the background shape and Cmd/Ctrl + C > Cmd/Ctrl + F to copy and paste on top of itself. Knock out the fill of this new shape and change the stroke colour values to C – 0 M – 100 Y – 100 K – 32. Thicken the stroke to 10px.
In the menu bar, click Effect. Don’t then click Apply Gaussian Blur, as this will use the last-used settings. We want to use slightly different settings for the shading – click Gaussian Blur and set the radius to 40px.
In the Transparency palette, change the blending mode to Multiply and reduce the opacity to 90%.
Double-click on an empty space to exit the group. Then, holding down Alt/Opt + Shift, click and drag a copy of the group directly above the original. Make it slightly smaller and place behind the original group by hitting Cmd/Ctrl + [.
Double-click the new group to enter it, then select the background shape and change the fill to a deeper orange. You may find it difficult to select the background shape as the Gaussian Blur effect on the shading may overlap it: to get around this, place the shading line at the back of the group by selecting it and hitting Cmd/Ctrl + Shift + [, and then change the colour of the background shape, before placing it at the back again by selecting it and hitting Cmd/Ctrl + Shift + [.