How would I make an indent that runs on all sides of the object? I'm trying to make an old PC monitor and there is a seam that runs all around. I tried Extruding inwards but since it runs on all sides it just goes in one direction. Sorry.. still learning Blender. What should I do?

Also should I be using inset and extrude for the smaller heat vents? Or is there a better way to go about it?
You can simply Inset the faces

Select your loop
Inset it by 0, set depth as desired
Check Offset Even