I would like to have one those button filled with colour with green instead of outlined button like here http://blueowlcreative.com/wp/fortuna/buttons/

Can I archive it somehow? Thank you

Sure you can, you can simply style your CSS entry appropriately, for example:

#menu > ul > li.boc_nav_button a {
    background: #08ada7;
    border: 2px solid #08ada7;
    color: #fff;
}