.header {
  position: sticky;
  top: 0;
  left: 0;
  width: 100%;
  height: 100px;
  background-color: #ffffff;
  z-index: 100;
}
.header_scrolled {
  -webkit-box-shadow: 0px 16px 14px -11px rgba(0, 0, 0, 0.07);
  -moz-box-shadow: 0px 16px 14px -11px rgba(0, 0, 0, 0.07);
  box-shadow: 0px 16px 14px -11px rgba(0, 0, 0, 0.07);
}

.menu > img {
  display: block;
  position: absolute;
  top: 25px;
  left: 25px;
  cursor: pointer;
}

.side_menu {
  position: fixed;
  left: -400px;
  top: 0;
  width: 400px;
  height: 100%;
  background-color: #ffffff;
  z-index: 150;
  padding-top: 10px;
  padding-left: 10px;
  overflow-y: auto;
  -webkit-box-shadow: 4px 0px 9px 2px rgba(0, 0, 0, 0.05);
  -moz-box-shadow: 4px 0px 9px 2px rgba(0, 0, 0, 0.05);
  box-shadow: 4px 0px 9px 2px rgba(0, 0, 0, 0.05);
}

@media all and (max-width: 900px) {
  .header {
    height: 50px;
  }

  .header_scrolled {
    -webkit-box-shadow: 0px 10px 12px 0px rgba(0, 0, 0, 0.05);
    -moz-box-shadow: 0px 10px 12px 0px rgba(0, 0, 0, 0.05);
    box-shadow: 0px 10px 12px 0px rgba(0, 0, 0, 0.05);
  }
  .menu > img {
    top: 10px;
    left: 10px;
    height: 30px;
    width: 30px;
    background-size: 30px 30px;
  }

  .side_menu {
    left: -200px;
    width: 200px;
  }
}