@media only screen and (max-width: 991px) {
  .inner_material_article {
    -webkit-flex-direction: column;
    -ms-flex-direction: column;
    flex-direction: column;
  }
  .list_material_left {
    width: 100%;
    margin-bottom: 30px;
    display:none;
  }
  .article_material {
    width: 100%;
    text-align: center;
    padding: 0;
  }
  .photo_material img {
    width: auto;
    height: auto;
    max-width: 100%;
  }
}
@media only screen and (max-width: 585px) {
  .nav_pages {
    -webkit-flex-direction: column;
    -ms-flex-direction: column;
    flex-direction: column;
    -ms-align-items: center;
    align-items: center;
  }
  .nav_pages span {
    display: none;
  }
  .nav_pages  a {
    display: block;
    margin-bottom: 10px;
  }
  .head_material_page{
    -webkit-flex-direction: column;
    -ms-flex-direction: column;
    flex-direction: column;
    -ms-align-items: center;
    align-items: center;
    padding-right: 0;
  }
  .head_material_page h3 {
    margin-right: 0;
    margin-bottom: 20px;
    padding-right: 20px;
    padding-left: 20px;
    width: 100%;
  }
}