diff --git a/src/js/page.js b/src/js/page.js
index 087f464..78326d4 100644
--- a/src/js/page.js
+++ b/src/js/page.js
@@ -11,7 +11,6 @@ document.addEventListener("DOMContentLoaded", function() {
   let current_selected_toc = null
   let current_intersectiong_entry = null
   const observer = new window.IntersectionObserver(entries => {
-    console.log(entries)
     entries.some(entry => {
       // console.log('observe')
       // Add 'active' class if observation target is inside viewport
@@ -20,23 +19,32 @@ document.addEventListener("DOMContentLoaded", function() {
       console.log('before')
       console.log('entry', entry)
       console.log('current', current_intersectiong_entry)
-      if (current_intersectiong_entry === null && entry.isIntersecting) {
-        let res = findCorrespondingTocTitle(entry.target)
-        res.parentElement.classList.add('bg-blue-800');
-        current_intersectiong_entry = entry
-        return true;
+      if (entry.isIntersecting) {
+        if (current_intersectiong_entry === null) { // first page load
+          let res = findCorrespondingTocTitle(entry.target)
+          res.parentElement.classList.add('bg-blue-800');
+          current_intersectiong_entry = entry
+          return true;
+        }
+        if (current_intersectiong_entry.boundingClientRect.y < 0) { //previous selected is out of viewport
+          current_intersectiong_entry.target.classList.remove('bg-blue-800');
+          let res = findCorrespondingTocTitle(entry.target) //First intersection entry
+          res.parentElement.classList.add('bg-blue-800');
+          current_intersectiong_entry = entry
+          return true;
+        }
       }
       console.log('after')
       console.log('entry', entry)
       console.log('current', current_intersectiong_entry)
-      if (entry.isIntersecting === false) { //some section got out of viewport remove its active class and add to next sibling
-        let res = findCorrespondingTocTitle(entry.target) //First intersection entry
-        res.parentElement.classList.remove('bg-blue-800');
-        res.parentElement.nextElementSibling.classList.add('bg-blue-800');
-        current_intersectiong_entry = entry
-        return true;
-        // current_intersectiong_entry = null
-      }
+      // if (entry.isIntersecting === false) { //some section got out of viewport remove its active class and add to next sibling
+      //   let res = findCorrespondingTocTitle(entry.target) //First intersection entry
+      //   res.parentElement.classList.remove('bg-blue-800');
+      //   res.parentElement.nextElementSibling.classList.add('bg-blue-800');
+      //   current_intersectiong_entry = entry
+      //   return true;
+      //   // current_intersectiong_entry = null
+      // }
       // current_intersectiong_entry = entry
 
       // if (current_intersectiong_entry !== null && current_intersectiong_entry.target === entry.target && entry.isIntersecting === false) {
diff --git a/static/js/page.js b/static/js/page.js
index 3072e44..cac0a03 100644
--- a/static/js/page.js
+++ b/static/js/page.js
@@ -1 +1 @@
-function findCorrespondingTocTitle(n){return[...document.querySelectorAll("#toc li a")].find(e=>e.href.substring(e.href.indexOf("#"))==="#"+n.id)}document.addEventListener("DOMContentLoaded",function(){document.getElementById("navbar").clientHeight,document.getElementById("toc");var e=document.querySelectorAll("#toc li a");document.getElementById("page-content");let t=null;const n=new window.IntersectionObserver(e=>{console.log(e),e.some(n=>{if(console.log("before"),console.log("entry",n),console.log("current",t),null===t&&n.isIntersecting){let e=findCorrespondingTocTitle(n.target);return e.parentElement.classList.add("bg-blue-800"),t=n,!0}if(console.log("after"),console.log("entry",n),console.log("current",t),!1===n.isIntersecting){let e=findCorrespondingTocTitle(n.target);return e.parentElement.classList.remove("bg-blue-800"),e.parentElement.nextElementSibling.classList.add("bg-blue-800"),t=n,!0}})},{root:null,threshold:.1});var o=[];[...e].forEach(e=>{o.push(e.href.substring(e.href.indexOf("#")))});const l=document.querySelectorAll(o.join(","));l.forEach(e=>{n.observe(e)})});
\ No newline at end of file
+function findCorrespondingTocTitle(n){return[...document.querySelectorAll("#toc li a")].find(e=>e.href.substring(e.href.indexOf("#"))==="#"+n.id)}document.addEventListener("DOMContentLoaded",function(){document.getElementById("navbar").clientHeight,document.getElementById("toc");var e=document.querySelectorAll("#toc li a");document.getElementById("page-content");let t=null;const n=new window.IntersectionObserver(e=>{e.some(n=>{if(console.log("before"),console.log("entry",n),console.log("current",t),n.isIntersecting){if(null===t){let e=findCorrespondingTocTitle(n.target);return e.parentElement.classList.add("bg-blue-800"),t=n,!0}if(t.boundingClientRect.y<0){t.target.classList.remove("bg-blue-800");let e=findCorrespondingTocTitle(n.target);return e.parentElement.classList.add("bg-blue-800"),t=n,!0}}console.log("after"),console.log("entry",n),console.log("current",t)})},{root:null,threshold:.1});var o=[];[...e].forEach(e=>{o.push(e.href.substring(e.href.indexOf("#")))});const r=document.querySelectorAll(o.join(","));r.forEach(e=>{n.observe(e)})});
\ No newline at end of file