Another design based on a box template from Package Form and Design.
The original had a heart on the top but I switched it to a shamrock to make it a bit more seasonal.
Download and cut out template
Inkscape SVG NEW file. Score lines deleted. Nodes joined. Does it cut properly now?
Score and crease all fold lines.
Tuck side tabs into side slots. Glue or tape if you wish.
Look at the bottom flaps. Two are the same, one is U shaped and one is long. Close the flaps in this order: U shaped, then the pair that are the same. Now push these three into the box slightly. Poke the long flap into the slot formed by the other flaps. The long flap goes under the U shaped flap.
Close the top of the box.
Bend each top flap slightly and slide it under the shamrock. The stem of the shamrock will be in the slots in the flaps.
Slide the small tabs into the small slots. You may have to enlarge the slots slightly (stick a scissor blade in and push to one side and then the other) if your paper is thick.