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ecss nearly:  

<!-- tab module -->
<section class="ns-TabsModule" data-active-tab="A">
  <!-- horizontal scroll wrapper -->
  <div class="ns-ScrollWrapper">
    <!-- tab nav -->
    <nav class="ns-TabNav">
      <a href="#ns-TabPanelA" class="ns-TabNav_Link" data-tab="A"><span>A</span></a>
      <a href="#ns-TabPanelB" class="ns-TabNav_Link" data-tab="B"><span>Black Eyed</span></a>
      <a href="#ns-TabPanelC" class="ns-TabNav_Link" data-tab="C"><span>Dog</span></a>
      <a href="#ns-TabPanelD" class="ns-TabNav_Link" data-tab="D"><span>He</span></a>
      <a href="#ns-TabPanelE" class="ns-TabNav_Link" data-tab="E"><span>Called</span></a>
      <a href="#ns-TabPanelF" class="ns-TabNav_Link" data-tab="F"><span>At</span></a>
      <a href="#ns-TabPanelG" class="ns-TabNav_Link" data-tab="G"><span>My Door</span></a>
      <span class="ns-TabNav_Indicator"></span>
    </nav><!-- /.ns-TabNav -->
  </div><!-- /.ns-ScrollWrapper -->
  <!-- tab panels -->
  <div class="ns-TabPanels">
    <div class="ns-TabPanel" id="ns-TabPanelA" data-tab-panel="A">Panel A</div>
    <div class="ns-TabPanel" id="ns-TabPanelB" data-tab-panel="B">Panel B</div>
    <div class="ns-TabPanel" id="ns-TabPanelC" data-tab-panel="C">Panel C</div>
    <div class="ns-TabPanel" id="ns-TabPanelD" data-tab-panel="D">Panel D</div>
    <div class="ns-TabPanel" id="ns-TabPanelE" data-tab-panel="E">Panel E</div>
    <div class="ns-TabPanel" id="ns-TabPanelF" data-tab-panel="F">Panel F</div>
    <div class="ns-TabPanel" id="ns-TabPanelG" data-tab-panel="G">Panel G</div>
  </div><!-- /.ns-TabPanels -->
</section><!-- /.ns-TabsModule -->


                @use postcss-nested;
@use postcss-simple-vars;

$base-unit: 11px;
$indicator-speed: 0.2s;

.ns-TabsModule {
  width: 100%;
  text-align: center;

.ns-TabNav {
  position: relative;
  /* wipe out any unwanted whitespace around inline elements */
  font-size: 0;

.ns-TabNav_Link {
  display: inline-block;
  margin: 0 $base-unit;
  text-decoration: none;
  font-size: 12px;
  line-height: calc($base-unit * 4);
  color: #bbb;
  text-transform: uppercase;
  span {
    font-size: inherit;
    line-height: inherit;
    letter-spacing: 1px;
    pointer-events: none;

.ns-TabNav_Indicator {
  position: absolute;
  bottom: 0;
  left: 0;
  width: 100px;
  height: 2px;
  background-color: indianred;
  transition-property: transform, left, background-color;
  transition-duration: $indicator-speed;
  transform-origin: 0;
  transform: translate3d(0, 0, 0) scaleX(0);
  opacity: 0;
  animation: fadeMeIn $indicator-speed forwards;
  animation-delay: $indicator-speed;

.ns-TabPanel {
  padding: 40px;
  font-size: 11px;
  color: #505050;
  text-transform: uppercase;
  letter-spacing: 1px;
  display: none;

@keyframes fadeMeIn {
  to {
    opacity: 1;

/* prettify */

body {
  box-sizing: border-box;
  background: #222;
  height: 100vh;
  overflow: hidden;
  padding-top: 100px;
  text-rendering: optimizeLegibility;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;

.ns-ScrollWrapper {
  overflow-x: scroll;
  overflow-y: hidden;
  -webkit-overflow-scrolling: touch;
  white-space: nowrap;
  box-shadow: inset 0 -2px 0 0 #404040;
  &::-webkit-scrollbar {
    display: none;

* indicator color for each tab should you need,
* could attach data-color attribute to tab link instead, JS maybe 
* performance should dictate what to do
.ns-TabNav_Indicator {
  [data-active-tab="B"] & { background-color: black; }
  [data-active-tab="C"] & { background-color: mediumaquamarine; }
  [data-active-tab="D"] & { background-color: slateblue; }
  [data-active-tab="E"] & { background-color: coral; }
  [data-active-tab="F"] & { background-color: indianred; }
  [data-active-tab="G"] & { background-color: $color-white; }



                "use strict";
//tab menu w/tab panel behaviour
//still learning. be kind. 

//get tabs module parent
var tabsModule = document.body.querySelector(".ns-TabsModule");
//get tab nav
var tabNavList = document.body.querySelector(".ns-TabNav");
//get all tab nav links
var tabNavLinks = document.querySelectorAll(".ns-TabNav_Link");
//get tab nav current nav link indicator
var tabNavCurrentLinkindicator = tabNavList.querySelector(".ns-TabNav_Indicator");
//get all tab panels
var tabPanels = document.querySelectorAll(".ns-TabPanel");
//show tab panel A first because panel A nav link has indicator on page load
document.getElementById("ns-TabPanelA").style.display = "block";

* position indicator function
function positionIndicator() {
  //get left position of tab nav ul
  var tabNavListLeftPosition = tabNavList.getBoundingClientRect().left;
  //get tab module parent current data value
  var tabsModuleSectionDataValue = tabsModule.getAttribute("data-active-tab") || "A";
  //get nav link span with data value that matches current tab module parent data value
  var tabNavCurrentLinkText = tabNavList.querySelector("[data-tab='" + tabsModuleSectionDataValue + "'] span");
  //get dimensions of current nav link span
  var tabNavCurrentLinkTextPosition = tabNavCurrentLinkText.getBoundingClientRect();
  //set indicator left position via CSS transform
  //current nav link span left position - tab nav ul left position
  //prefix me for live =
    "translate3d(" +
    (tabNavCurrentLinkTextPosition.left - tabNavListLeftPosition) +
    "px,0,0) scaleX(" +
    tabNavCurrentLinkTextPosition.width * 0.01 +

* hide all tab panels function
function hideAllTabPanels() {
  //loop through all tab panel elements
  for (i = 0; i < tabPanels.length; i++) {
    //remove style attribute from all tab panels to hide them

* tab nav link function
* tab nav link event displays matching tab panel,
* and positions current tab nav link indicator
var tabNavLinkEvent = function() {
  //get this link data value
  var thisLink = this.getAttribute("data-tab");
  //get this link href value
  var thisHref = this.getAttribute("href");
  //get tab panel element with ID that matches this link href value
  var thisTabPanel = document.querySelector(thisHref);
  //set tab module parent data to this link data value
  tabsModule.setAttribute("data-active-tab", thisLink);
  //fire hide all tab panels function
  //get tab panel element with ID that matches this link href value and set its style to show it = "block";
  //fire the position indicator function

* attach tabNavLinkEvent to all tab nav links
* loop through all nav links and add event
* need to change to parent element and use maybe
for (var i = 0; i < tabNavLinks.length; i++) {
  //for each nav link, add click event that fires tab nav link click event function
  tabNavLinks[i].addEventListener("click", tabNavLinkEvent, false);

* should really position indicator from parent left edge rather than body, 
* to keep indicator in position on resize. meh
* for now, here's a quick win because i'm tired 
(function() {
  //someone smarter than me "debounce" code
  var resizeTimeout;
  function resizeThrottler() {
    if (!resizeTimeout) {
      resizeTimeout = setTimeout(function() {
        resizeTimeout = null;
      }, 66);
  //function to fire after resize timeout delay
  function actualResizeHandler() {
    //fire the position indicator function
  //window resize event
  window.addEventListener("resize", resizeThrottler, false);

* fire position indicator function right away

//this is old code
//make your own from this for the fun of it :)
//p.s. i'm getting better.

* listen to nick drake for peace of mind