The transport controls are the row of buttons at the top (or bottom!) of the theme.
Stop, Previous, Play, and Next are always shown. The Randomize, Volume, and Reload Theme buttons can only be toggled on or off in the Options » Transport controls menu:
The Transport button size and spacing can be adjusted in the Transport controls menu if they are too big or too small for your liking.
By default, the Transport controls appear above the artwork, however in the Transport controls menu they can be moved below the artwork. This might look better, but due to space restrictions it will slightly shrink the available area of the artwork.
If you control playback through a remote control, or some other external program, the transport controls can be completely hidden as well.