diff --git a/mods/outliner/app.css b/mods/outliner/app.css
index 700dcff..dd6b19d 100644
--- a/mods/outliner/app.css
+++ b/mods/outliner/app.css
@@ -4,7 +4,7 @@
  * (c) 2020 CloudHill
  * under the MIT license
  */
- 
+
 .outliner {
   max-height: 100%;
   overflow: hidden auto;
@@ -29,7 +29,7 @@
   line-height: 2.2;
   color: inherit;
   text-decoration: none;
-  
+
   white-space: nowrap;
   overflow: hidden;
   text-overflow: ellipsis;
@@ -48,4 +48,19 @@
 }
 .outline-header.notion-sub_sub_header-block a {
   text-indent: 36px;
-}
\ No newline at end of file
+}
+
+.outliner[lined] .notion-sub_header-block::before,
+.outliner[lined] .notion-sub_sub_header-block::before {
+  content: "";
+  border-left: solid 1px;
+  height: 2.2em;
+  opacity: 0.25;
+  position: absolute;
+  left: 18px;
+  pointer-events: none;
+}
+.outliner[lined] .notion-sub_sub_header-block::before {
+  border-right: solid 1px;
+  width: 18px;
+}
diff --git a/mods/outliner/mod.js b/mods/outliner/mod.js
index 5338973..56efa89 100644
--- a/mods/outliner/mod.js
+++ b/mods/outliner/mod.js
@@ -17,6 +17,12 @@ module.exports = {
   version: '1.0.0',
   author: 'CloudHill',
   options: [
+    {
+      key: 'lined',
+      label: 'indentation lines',
+      type: 'toggle',
+      value: true
+    },
     {
       key: 'fullHeight',
       label: 'full height',
diff --git a/mods/outliner/panel.js b/mods/outliner/panel.js
index 623a821..00ed19e 100644
--- a/mods/outliner/panel.js
+++ b/mods/outliner/panel.js
@@ -64,6 +64,7 @@ module.exports = (store) => {
     const outline = document.querySelector('.outliner');
     if (!outline) return;
     outline.textContent = '';
+    if (store.lined) outline.setAttribute('lined', '');
 
     const pageContent = document.querySelector('.notion-page-content');
     const headerBlocks = pageContent.querySelectorAll('[class*="header-block"]');
@@ -77,7 +78,6 @@ module.exports = (store) => {
             placeholder="${placeholder}">${block.innerText}</a>
         </div>
       `);
-
       outline.append(header);
     })
   }