See the MDN docs for the available values for border-style
:
- none : No border, sets width to 0.
This is the default value.
- hidden : Same as 'none', except in terms of
border conflict resolution for table
elements.
- dashed : Series of short
dashes or line segments.
- dotted :
Series of dots.
- double : Two straight
lines that add up to the pixel amount
defined as border-width.
- groove :
Carved effect.
- inset : Makes the box
appear embedded.
- outset : Opposite of
'inset'. Makes the box appear 3D
(embossed).
- ridge : Opposite of
'groove'. The border appears 3D
(coming out).
- solid : Single,
straight, solid line.
Apart from those choices, there is no way to influence the standard border's style.
If the possibilities there are not to your liking, you could use CSS3's border-image
but note that browser support for this is still very spotty (EDIT: browser support is good as of 2020).