function changeGfx(gfx_id) {
    document.getElementById('header_gfx').style.background = "url('http://abstractive.plimg/gfx/gfx_"+gfx_id+".jpg') no-repeat";
}

function mainGfx() {
    document.getElementById('header_gfx').style.background = "url('http://abstractive.pl/img/gfx/gfx.jpg') no-repeat";
}

function showHide(id) {
  document.getElementById(id).style.visibility = (document.getElementById(id).style.visibility == "visible") ? "hidden" : "visible"
  document.getElementById(id).style.position = (document.getElementById(id).style.position == "static") ? "absolute" : "static"
}