Stainless steel is a type of steel alloy that contains chromium, which gives it its characteristic resistance to rust and corrosion. The reason why magnets don't stick to your stainless steel fridge is that stainless steel is not ferromagnetic.
Ferromagnetic materials, like iron, nickel, and cobalt, are attracted to magnets and can be magnetized themselves. When a magnet comes close to a ferromagnetic material, the atoms within the material align in a way that creates a magnetic field, causing the material to be attracted to the magnet.
Stainless steel, on the other hand, is composed of a mix of elements, including iron, but the addition of chromium and other elements in the alloy alters the structure in a way that it is not ferromagnetic. The arrangement of its atoms does not allow it to generate a magnetic field in response to an external magnetic field. As a result, magnets do not stick to stainless steel surfaces.
However, it's worth noting that there are some types of stainless steel that have a small amount of ferromagnetic properties. These are known as "magnetic stainless steels" and are used in certain applications where magnetic properties are desired. But for most standard stainless steel fridges, magnets won't stick due to their non-ferromagnetic nature.