.itemtab_area {
  display: flex;
  flex-wrap: wrap;
  width: 100%;
  margin: auto;
}

.itemtab_class {
  display: block;
  order: -1;
  float: left;
  width: calc(100%/3);
  height: 50px;
  border-bottom: 1px solid #ccc;
  /* background-color: darkgrey; */
  font-size: 16px;
  line-height: 50px;
  text-align: center;
}

input[name='itemtab_name'] {
  display: none;
}


input:checked+.itemtab_class {
  border-bottom: 1px solid #000;
  background-color: #efefef;
}

@media screen and (max-width: 599px) {
  input:checked+.itemtab_class {
    text-underline-offset: none;
  }
}

.itemcontent_class {
  display: none;
  width: 100%;
}

input:checked+.itemtab_class+.itemcontent_class {
  display: block;
}