How do I build floating shelves for my bathroom?

Here's a post that might help you - https://www.makingmanzanita.com/floating-shelves-for-extra-bathroom-storage/

Fairly easy floating shelves video

https://www.youtube.com/watch?v=wki3wMAbtLg

Here are some ideas on Hometalk: https://www.hometalk.com/search/posts?filter=floating%20shelves%20bathroom

If you only need to support a modicum of weight, find your wall studs. Take a 1x3 or 1x4 straight and true piece of lumber and cut to the length you want (must be long enough to include 2 studs, 3 is better). Stain, paint or finish the shelf as you wish. Mark the stud locations on the face that will go against the wall. Cut the heads off the appropriate number of 16p nails. Use a 1/8" drill bit and drill the shelf to 1/3 depth of the length of the nail. Insert the nails into the holes, point out. Place the board (with nails) against the wall making sure the shelf is level. Gently tap the front of the shelf so the nails mark the locations on the wall. Use the 1/8" bit to drill the wall. Place the shelf against the wall with the nails started in the new holes and gently tap into place. Floating shelf, no brackets, corbels or braces.

If you're a wood worker, here's how its done.... https://www.youtube.com/watch?v=pVyr73P-eV0&t=108s

Me I'm going to Ikea... https://www.ikea.com/ms/en_US/usearch/?query=floating%20shelves two colors, white and black-brown

Many of the big box stores also carry these now.... https://www.google.com/search?client=opera&q=floating+shelves+lowes&sourceid=opera&ie=UTF-8&oe=UTF-8