The dotted gray line is the border box
dotted	dashed	solid	double
groove	ridge	inset	outset

partial attributes merged

outline:thin solid red;

outline:red thin solid;

{ outline:thin solid; }{outline:blue; } (merged, reset all - color has no effect)

{ outline:thin solid; }{outline-color:green; } (merged, overwrite only color)

{ outline:thin solid; }{outline:blue; } (merged, reset all - color has no effect)

{ outline:thin solid; }{outline-color:green; } (merged, overwrite only color)

{ outline:thin blue solid; }{outline-color:green; } (merged, overwrite only color)

{ outline:thin blue solid; }{outline-style:dashed; } (merged, overwrite only style)

{ outline:thin blue solid; }{outline-width:thick; } (merged, overwrite only width)

{ outline:thin blue solid; }{outline-width:medium; } (merged, overwrite only width)

{ outline:thin blue solid; }{outline-width:3pt; } (merged, overwrite only width)