src/main/java/org/fit/layout/cssbox/BoxNode.java
@Override
    public int getTopBorder()
    {
        Box box = getBox();
        if (box instanceof ElementBox)
            return ((ElementBox) box).getBorder().top;
        else
            return 0;
    }
@Override
    public int getTopBorder()
    {
        Box box = getBox();
        if (box instanceof ElementBox)
            return ((ElementBox) box).getBorder().top;
        else
            return 0;
    }
Obtains the top border of the box
@return the width of the border or 0 when there is no border