Fix the compatibility of the smooth scrolling in Safari

Safari(at least on v14) does not support CSS property `scroll-behavior`

assets/js/_utils/smooth-scroll.js

@@ -0,0 +1,42 @@
+/*
+  Safari doesn't support CSS `scroll-behavior: smooth`,
+  so here is a compatible sollution for all browser to smooth scrolling
+
+  See: <https://css-tricks.com/snippets/jquery/smooth-scrolling/>
+
+  Warning: It must be called after all `<a>` tags (e.g., the dynamic TOC) are ready.
+*/
+
+$(function() {
+  $("a[href*='#']")
+    .not("[href='#']")
+    .not("[href='#0']")
+    .click(function(event) {
+
+    if (location.pathname.replace(/^\//, "") === this.pathname.replace(/^\//, "")
+      && location.hostname === this.hostname) {
+
+      var target = $(decodeURI(this.hash));
+
+      if (target.length) {
+
+        event.preventDefault();
+
+        $("html, body").animate({
+          scrollTop: target.offset().top
+        }, 800, function() {
+          var $target = $(target);
+          $target.focus();
+
+          if ($target.is(":focus")) { /* Checking if the target was focused */
+            return false;
+          } else {
+            $target.attr("tabindex", "-1"); /* Adding tabindex for elements not focusable */
+            $target.focus(); /* Set focus again */
+          }
+        });
+      }
+    }
+
+  }); /* click() */
+});