add a border to a div css

CSS
p.dotted {border-style: dotted;}
p.dashed 
{border-style: dashed;}
p.solid {border-style: solid;}
p.double 
{border-style: double;}
p.groove {border-style: groove;}
p.ridge 
{border-style: ridge;}
p.inset {border-style: inset;}
p.outset 
{border-style: outset;}
p.none {border-style: none;}
p.hidden {border-style: hidden;}

p.mix {border-style: dotted dashed solid double;} border-style: /*Style Prefered*/;

/*Styles can be:

dotted
dashed
solid
double
groove
ridge
inset
outset
nonce
hidden

*/
Source

Also in CSS: