In brief
border-style chooses a border type such as solid, dashed or dotted. none means no border rather than a line that is merely transparent.
Useful to know
border-style chooses a border type such as solid, dashed or dotted. none means no border rather than a line that is merely transparent. [1]
For component states, check geometry too: enabling a border can alter dimensions according to box-sizing. Evaluate style changes together with keeping the layout stable.
Sources
For further detail and to check the information: