.whole {
  width: 100%;
}
.threequarter {
  width: 75%;
}
.twothird {
  width: 66.6666%;
}
.half {
  width: 50%;
}
.third {
  width: 33.3333%;
}
.quarter {
  width: 25%;
}

.widescreen {
  display: block;
}
.narrowscreen {
  display: none;
}

@media only screen and (max-width: 750px) {
  .whole,
  .threequarter,
  .twothird,
  .half,
  .third,
  .quarter,
  .column_left,
  .column_main,
  .column_right {
    width: 100%;
  }

  .widescreen {
    display: none;
  }
  .narrowscreen {
    display: block;
  }

  .menutop {
    background-position: center;
  }
}