When I made my post I was thinking casual short sleeve button down like this one, except with shorts, which I think is fine. I prefer simpler prints but you’ll often see these with all kinds of wacky prints or in plaid etc.
The type of shirt that is meant to worn untucked.
For a casual long sleeve with shorts I was thinking something like this, I prefer ones that can be worn untucked but it depends on your style.
Dress shirts for me typically are a little more formal looking, often thicker material and always must be tucked in due to the cut and fit.