Sue had some small gaps between her steps and the walls:
I suggested a small skirt. First I templated it with cardboard and paper and tape:
Next I bought a sheet of 1/2″ MDF and ripped it into 8″ strips. I only needed them to be about 6 feet long. I transferred the template onto the boards and cut them at my workshop with a sliding mitre saw and a jigsaw. I gave the top edge a small round and primed them white. Then I installed them (with a few adjustments), secured to the wall with brad nails, and caulked with white Dap.