`border` property invalid when shorthand filter used

[kdzwinel]

When nodes border isn't the same for all edges getComputedStyle returns empty value for shorthand property border. It make sense because border property does allow setting only one style of border for all edges.

Workaround needed.

https://developer.mozilla.org/en-US/docs/Web/CSS/border

[kdzwinel]

Note to self:

if(border === '') {
  for(style in [borderTop, borderLeft, borderBottom, borderRight]) {
    if(style !== '') {
      output += style;
    }
  }
}