custom class on tab ALB is : steviger-test

just fill in like you are used to in a tab ALB element

.tabcontainer.sidebar_tab.steviger-test:before {
  display: block;
  width: 45%;
  height: 100%;
  content: "";
  position: absolute;
  background-color: #cfe7d1;
}

.tabcontainer.sidebar_tab.steviger-test * {
  border: none !important
}

.sidebar_tab.steviger-test .tab_titles {
  width: 45% !important;
  max-width: unset; 
  margin-right: 5%;
  height: 100% !important;
  max-height: unset !important;
  background-color: #cfe7d1;
  overflow: visible;
}

.sidebar_tab.steviger-test .tab_titles .tab {
  width: 50%;
}

.sidebar_tab.steviger-test .tab_titles .active_tab  {
  background-color: rgba(255,255,255,0.3);
  width: 50%;
}

.sidebar_tab.steviger-test .tab_content {
  background-color: #fbf0d0 !important;
}

.sidebar_tab.steviger-test .tab_titles span.left,
.sidebar_tab.steviger-test .tab_titles span.right {
  width: 50%;
  display: inline-table;
}


@media only screen and (max-width: 767px) {
  .tabcontainer.sidebar_tab.steviger-test:before {
    display: block;
    width: 100%;
    background-color: #cfe7d1;
  }
  .responsive #top .main_color .tabcontainer.steviger-test .active_tab {
    background-color: #178d62 !important;
    color: #000;
    width: 100%;
  }
  .sidebar_tab.steviger-test .fullsize-tab span.left,
  .sidebar_tab.steviger-test .fullsize-tab span.right {
    width: 50%;
    display: inline-table;
  }
}

/*** maybe an icon in front of the active tab **/
.sidebar_tab.steviger-test .tab_titles .active_tab{
  padding-left: 20px
}

.sidebar_tab.steviger-test .tab_titles .active_tab:before {
  content: "\00BB";
  width: 30px !important;
  display: inline-block;
  position: absolute;
  left: 5px;
}