So, dryads are typically thin, but can vary some in thickness (luz and all); is it possible for Dryads to build a lot of muscle? Or would that be something a Dryad just wouldn't invest so much time in? I guess that brings the question of how concerned a Dryad is with their appearance (if it's of any significance). Sorry, these are weird questions, ah-- "does the concept of 'beauty' exist to a Dryad?" is the ultimate question here I suppose, ahah!
Dryads can build some muscle, but they tend to remain pretty wiry and ropey when they do, and their thick skin masks sharp definition. Dryads don’t really seek to build muscle on purpose since it carries no particular value to them.
Dryads do have a concept of beauty. Like humans, some individuals are just considered easier on the eyes. Many of the things about a Dryad’s physical appearance that make them look especially pretty aren’t really things they can do anything about, so they don’t concern themselves too much about it. Other things affect how beautiful a Dryad is perceived to be by other Dryads, some of which they can do something about - they focus on those things, generally.
For example, they can keep their tree in nice shape, pruning off dead branches and such, and they can keep the area around their tree manicured and decorated. They can also learn to move and walk in a quiet, graceful manner, since Dryads prize that.