Added animation to content tabs

material/base.html

@@ -34,7 +34,7 @@
       {% endif %}
     {% endblock %}
     {% block styles %}
-      <link rel="stylesheet" href="{{ 'assets/stylesheets/main.8e8281cd.min.css' | url }}">
+      <link rel="stylesheet" href="{{ 'assets/stylesheets/main.ffa0dd14.min.css' | url }}">
       {% if config.theme.palette %}
         {% set palette = config.theme.palette %}
         <link rel="stylesheet" href="{{ 'assets/stylesheets/palette.e6a45f82.min.css' | url }}">
@@ -213,7 +213,7 @@
       </script>
     {% endblock %}
     {% block scripts %}
-      <script src="{{ 'assets/javascripts/bundle.649a939e.min.js' | url }}"></script>
+      <script src="{{ 'assets/javascripts/bundle.1cbe63b4.min.js' | url }}"></script>
       {% for path in config["extra_javascript"] %}
         <script src="{{ path | url }}"></script>
       {% endfor %}

src/assets/javascripts/components/content/tabs/index.ts

@@ -29,12 +29,14 @@ import {
   map,
   mapTo,
   merge,
+  startWith,
   tap
 } from "rxjs"
 
 import {
   getElement,
   getElementOffset,
+  getElementSize,
   getElements
 } from "~/browser"
 
@@ -65,14 +67,18 @@ export interface ContentTabs {
 export function watchContentTabs(
   el: HTMLElement
 ): Observable<ContentTabs> {
-  return merge(...getElements(":scope > input", el)
-    .map(input => fromEvent(input, "change")
+  const inputs = getElements(":scope > input", el)
+  return merge(...inputs.map(input => fromEvent(input, "change")
     .pipe(
       mapTo<ContentTabs>({
         active: getElement(`label[for=${input.id}]`)
       })
     )
-    )
+  ))
+    .pipe(
+      startWith({
+        active: getElement(`label[for=${inputs[0].id}]`)
+      } as ContentTabs)
     )
 }
 
@@ -94,12 +100,29 @@ export function mountContentTabs(
   const container = getElement(".tabbed-labels", el)
   return defer(() => {
     const push$ = new Subject<ContentTabs>()
-    push$.subscribe(({ active }) => {
-      const { x } = getElementOffset(active)
+    push$.subscribe({
+
+      /* Handle emission */
+      next({ active }) {
+        const offset = getElementOffset(active)
+        const { width } = getElementSize(active)
+
+        /* Set tab indicator offset and width */
+        el.style.setProperty("--md-indicator-x", `${offset.x}px`)
+        el.style.setProperty("--md-indicator-width", `${width}px`)
+
+        /* Smoothly scroll container */
         container.scrollTo({
           behavior: "smooth",
-        left: x
+          left: offset.x
         })
+      },
+
+      /* Handle complete */
+      complete() {
+        el.style.removeProperty("--md-indicator-x")
+        el.style.removeProperty("--md-indicator-width")
+      }
     })
 
     /* Create and return component */

src/assets/stylesheets/main/extensions/pymdownx/_tabbed.scss

@@ -87,6 +87,27 @@
       display: contents;
     }
 
+    // [js]: Show animated tab indicator
+    .js & {
+      position: relative;
+
+      // Tab indicator
+      &::after {
+        position: absolute;
+        bottom: 0;
+        display: block;
+        width: var(--md-indicator-width);
+        height: 2px;
+        background: var(--md-accent-fg-color);
+        transform: translateX(var(--md-indicator-x));
+        transition:
+          width     250ms,
+          transform 250ms;
+        transition-timing-function: cubic-bezier(0.4, 0, 0.2, 1);
+        content: "";
+      }
+    }
+
     // Webkit scrollbar
     &::-webkit-scrollbar {
       display: none;                   // Chrome, Safari
@@ -207,9 +228,13 @@
   // [screen]: Show active state
   @media screen {
     color: var(--md-accent-fg-color);
+
+    // [no-js]: Show border (indicator is animated with JavaScript)
+    .no-js & {
       border-color: var(--md-accent-fg-color);
     }
   }
+}
 
 // Tab label on keyboard focus placeholder
 %tabbed-label-focus-visible {