A first aid kit or wall mounted medicine cabinet can be mounted on a bathroom wall behind the bathroom mirror. The mirror is then foldable to the wall and open to access the contents of the cabinet. It is a practical and convenient use of space that otherwise would not be used at all. Medicine cabinets are generally used to store frequent access bathroom items such as medicine, toothpaste or makeup. To install them, starting with measure the distance between the two posts that are inside the wall on each side of the hole being cut.
And if you have to cut a beam in the previous step, you need to either cut the end again or modify the horizontal pieces in the next step butt against it. Cut two pieces of two by four that fit horizontally between the two vertical posts closest to the hole. Slide wall mounted medicine cabinet on the wall so that the lower face of the upper part is removed and the upper face of the lower part is removed flush with the edge of the hole. Fix these horizontal pieces by driving the screws through their ends diagonally and into the posts they are bumping into.
Are you working with the new construction? Or for some other reason the vertical posts are exposed? It may be easier to drive the screws horizontally through the vertical posts at the ends of the horizontal pieces. Fit the wall mounted medicine cabinet in the hole and secure it by screwing through the wing on its edge and on the horizontal the parts just installed. Install the mirror over the kit by mounting the hinges on the edge of the medicine box or on the wall next to the kit, depending on the instructions for the particular hardware.