This is a small floating shelf and matching bracket I made in order to eliminate clutter in a bathroom which lacked storage space above the counter.
Its dimensions are 130x75x15mm which includes a small 2x2mm raised lip along the outer edge. The shelf's bracket insert has an extra depression to fit screws with larger/rounded heads.
I left the shelf free floating on the bracket - no screws on the underside to lock them together. As long as you mount the bracket tight and on level, there's no issue with sliding. However, if you wish to add a screw or two to the underside, please do leave a comment on how it works out.