diff --git a/src/components/SearchBar.tsx b/src/components/SearchBar.tsx
index d266f7d..9f21e50 100644
--- a/src/components/SearchBar.tsx
+++ b/src/components/SearchBar.tsx
@@ -35,7 +35,7 @@ export function SearchBar({ onSearch, onFocus, value }: Props) {
       />
       <div className={`actions`}>
         <button
-          className={`toggle-mode`}
+          className={`toggle-search-mode`}
           title="Toggle search mode"
           onClick={() => {
             const newMode = searchMode === 'regex' ? 'fuzzy' : 'regex'
diff --git a/src/components/SideBar.tsx b/src/components/SideBar.tsx
index 62bcf8c..b2b7fea 100644
--- a/src/components/SideBar.tsx
+++ b/src/components/SideBar.tsx
@@ -7,7 +7,11 @@ import { SideBarBodyWrapper } from 'components/SideBarBodyWrapper'
 import { ToggleShowButton } from 'components/ToggleShowButton'
 import { useConfigs } from 'containers/ConfigsContext'
 import { platform } from 'platforms'
-import { useGitHubAttachCopyFileButton, useGitHubAttachCopySnippetButton } from 'platforms/GitHub'
+import {
+  useGitHubAttachCopyFileButton,
+  useGitHubAttachCopySnippetButton,
+  useGitHubCodeFold,
+} from 'platforms/GitHub'
 import * as React from 'react'
 import { cx } from 'utils/cx'
 import * as DOMHelper from 'utils/DOMHelper'
@@ -98,6 +102,7 @@ export function SideBar() {
 
   useGitHubAttachCopyFileButton(configContext.value.copyFileButton)
   useGitHubAttachCopySnippetButton(configContext.value.copySnippetButton)
+  useGitHubCodeFold(configContext.value.codeFolding)
 
   usePJAX()
   useProgressBar()
diff --git a/src/components/settings/SettingsBar.tsx b/src/components/settings/SettingsBar.tsx
index 6f84007..3a29e78 100644
--- a/src/components/settings/SettingsBar.tsx
+++ b/src/components/settings/SettingsBar.tsx
@@ -15,6 +15,7 @@ const WIKI_HOME_LINK = 'https://github.com/EnixCoda/Gitako/wiki'
 export const wikiLinks = {
   compressSingletonFolder: `${WIKI_HOME_LINK}/Compress-Singleton-Folder`,
   changeLog: `${WIKI_HOME_LINK}/Change-Log`,
+  codeFolding: `${WIKI_HOME_LINK}/Code-folding`,
   copyFileButton: `${WIKI_HOME_LINK}/Copy-file-and-snippet`,
   copySnippet: `${WIKI_HOME_LINK}/Copy-file-and-snippet`,
   createAccessToken: `${WIKI_HOME_LINK}/Access-token-for-Gitako`,
@@ -29,18 +30,24 @@ function SettingsBarContent() {
   const useReloadHint = useStateIO<React.ReactNode>('')
   const { value: reloadHint } = useReloadHint
 
-  const moreFields: SimpleField<'copyFileButton' | 'copySnippetButton'>[] =
+  const moreFields: SimpleField<'copyFileButton' | 'copySnippetButton'|'codeFolding'>[] =
     platform === GitHub
       ? [
+          {
+            key: 'codeFolding',
+            label: 'Fold source code button',
+            wikiLink: wikiLinks.codeFolding,
+            tooltip: `Read more in Gitako's Wiki`,
+          },
           {
             key: 'copyFileButton',
-            label: 'Copy file shortcut',
+            label: 'Copy file button',
             wikiLink: wikiLinks.copyFileButton,
             tooltip: `Read more in Gitako's Wiki`,
           },
           {
             key: 'copySnippetButton',
-            label: 'Copy snippet shortcut',
+            label: 'Copy snippet button',
             wikiLink: wikiLinks.copySnippet,
             tooltip: `Read more in Gitako's Wiki`,
           },
diff --git a/src/platforms/GitHub/index.ts b/src/platforms/GitHub/index.ts
index 8af9ae4..b6dab28 100644
--- a/src/platforms/GitHub/index.ts
+++ b/src/platforms/GitHub/index.ts
@@ -8,6 +8,7 @@ import { sortFoldersToFront } from 'utils/treeParser'
 import * as API from './API'
 import * as DOMHelper from './DOMHelper'
 import * as URLHelper from './URLHelper'
+export { useGitHubCodeFold } from './useGitHubCodeFold'
 
 function processTree(tree: TreeNode[]): TreeNode {
   // nodes are created from items and put onto tree
diff --git a/src/platforms/GitHub/useGitHubCodeFold.tsx b/src/platforms/GitHub/useGitHubCodeFold.tsx
new file mode 100644
index 0000000..df71aae
--- /dev/null
+++ b/src/platforms/GitHub/useGitHubCodeFold.tsx
@@ -0,0 +1,162 @@
+import { platform } from 'platforms'
+import { useCallback, useEffect } from 'react'
+import { useOnPJAXDone } from 'utils/hooks/usePJAX'
+import { GitHub } from '.'
+
+const theCSSClassMark = 'gitako-code-fold-attached'
+const theCSSClassMarkWhenDisabled = 'gitako-code-fold-attached-disabled'
+const theCSSClassForHiddenLine = 'gitako-code-fold-hidden'
+const theCSSClassForToggleElement = 'gitako-code-fold-handler'
+const tableSelector = `.blob-wrapper table`
+const selectorOfLineNumber = `.blob-num`
+const selectorOfLineContent = `.blob-code`
+
+const theCSSClassForToggleElementOnActive = 'active'
+function init() {
+  type LineNumber = number // alias
+  const blocks: LineNumber[] = [] // startLine -> exclusiveEndLine
+  /**
+   * For example, given such input
+   *
+   * 0 |∇ line1
+   * 1 |∇   line2
+   * 2 |
+   * 3 |∇   line3
+   * 4 |      line4
+   * 5 |  line5
+   *
+   * blocks will be
+   * 0 -> 5
+   * 1 -> 3
+   * 2
+   * 3 -> 5
+   * 4
+   * 5
+   */
+
+  const table = document.querySelector(tableSelector)
+  const lineElements = Array.from(document.querySelectorAll([tableSelector, 'tr'].join(' ')))
+  if (!table || !lineElements.length) return
+  if (table.classList.contains(theCSSClassMark)) {
+    if (table.classList.contains(theCSSClassMarkWhenDisabled)) {
+      // reactivate
+      table.classList.remove(theCSSClassMarkWhenDisabled)
+    }
+    return
+  }
+  table.classList.add(theCSSClassMark)
+
+  // setup blocks
+  {
+    type Level = number // measured by leading whitespace amount
+    const stack: [Level, LineNumber][] = []
+
+    function trySeal(lineNumber: number, level: number) {
+      let ignoredTheHighestLevelItem = false
+      while (stack.length) {
+        const top = stack.pop()! // safe
+        const [$LineNumber, $level] = top
+
+        if ($level < level) {
+          stack.push(top)
+          break
+        } else if (!ignoredTheHighestLevelItem) {
+          ignoredTheHighestLevelItem = true
+        } else {
+          blocks[$LineNumber] = lineNumber
+        }
+      }
+      stack.push([lineNumber, level])
+    }
+
+    lineElements.forEach((element, lineNumber) => {
+      const text = element.querySelector(selectorOfLineContent)?.textContent || null
+      if (text === null) return
+
+      const level = getTextLevel(text)
+      if (level === -1) return
+
+      trySeal(lineNumber, level)
+    })
+
+    trySeal(lineElements.length, -1)
+  }
+
+  // attach toggle buttons
+  blocks.forEach((end, line) => {
+    if (!end) return
+
+    const toggleElement = document.createElement('div')
+    toggleElement.setAttribute('role', 'button')
+    toggleElement.classList.add(theCSSClassForToggleElement)
+
+    const lineNumberElement = lineElements[line].querySelector(selectorOfLineNumber)
+    lineNumberElement?.appendChild(toggleElement)
+  })
+
+  const foldLines = new Set<LineNumber>()
+  function toggleLine(line: number) {
+    // const lineElements = Array.from(document.querySelectorAll(lineSelector))
+    const element = lineElements[line]
+    element.classList.toggle(theCSSClassForToggleElementOnActive)
+    if (foldLines.has(line)) {
+      foldLines.delete(line)
+    } else {
+      foldLines.add(line)
+    }
+
+    const linesToHide = new Set<LineNumber>()
+    for (const line of foldLines.values()) {
+      const end = blocks[line]
+      for (let $line = line + 1; $line < end; $line++) linesToHide.add($line)
+    }
+
+    lineElements.forEach((element, i) => {
+      if (linesToHide.has(i)) element.classList.add(theCSSClassForHiddenLine)
+      else element.classList.remove(theCSSClassForHiddenLine)
+    })
+  }
+
+  table.addEventListener('click', e => {
+    if (e.target instanceof HTMLElement) {
+      if (e.target.classList.contains(theCSSClassForToggleElement)) {
+        const tr = e.target.parentElement?.parentElement
+        if (tr) {
+          toggleLine(lineElements.indexOf(tr))
+          e.stopPropagation()
+        }
+      }
+    }
+  })
+}
+
+function cancelToggleFeature() {
+  const table = document.querySelector(tableSelector)
+  table?.classList.add(theCSSClassMarkWhenDisabled)
+}
+
+function getTextLevel(text: string) {
+  const leading = countLeadingWhitespace(text)
+  return leading === text.length ? -1 : leading
+}
+
+function countLeadingWhitespace(text: string) {
+  let i = 0
+  for (; i < text.length; i++) {
+    // Mixed usage of space and table indentation? ¯\_(ツ)_/¯
+    if (!(text[i] === ' ' || text[i] === '\t' || text[i] === '\n')) break
+  }
+  return i
+}
+
+export function useGitHubCodeFold(active: boolean) {
+  const effect = useCallback(() => {
+    if (platform !== GitHub) return
+    if (active) {
+      init()
+      return () => cancelToggleFeature()
+    }
+  }, [active])
+  useEffect(effect, [effect])
+  useOnPJAXDone(effect)
+}
diff --git a/src/styles/index.scss b/src/styles/index.scss
index 374b9cd..8ca0eb0 100644
--- a/src/styles/index.scss
+++ b/src/styles/index.scss
@@ -13,6 +13,33 @@ $github-header-z-index: 32;
 $github-pull-request-float-header-z-index: 110;
 $minimal-z-index: max($github-header-z-index, $github-pull-request-float-header-z-index) + 1;
 
+@mixin interactive-background($default, $hover, $active) {
+  background-color: $default;
+  &:focus,
+  &:hover {
+    background-color: $hover;
+  }
+  &:active {
+    background-color: $active;
+  }
+}
+
+@mixin interactive-background-on-before($default, $hover, $active) {
+  &::before {
+    background-color: $default;
+  }
+  &:hover {
+    &::before {
+      background-color: $hover;
+    }
+  }
+  &:active {
+    &::before {
+      background-color: $active;
+    }
+  }
+}
+
 :root {
   --gitako-width: #{$side-bar-base-width};
 }
@@ -54,6 +81,117 @@ $minimal-z-index: max($github-header-z-index, $github-pull-request-float-header-
     }
   }
 
+  // code folding start
+  .blob-wrapper table .blob-num {
+    position: relative; // for positioning
+    min-width: 60px;
+    padding-right: 20px;
+  }
+
+  // cancel code fold if not wrapped with .gitako-code-fold-mark
+  .gitako-code-fold-handler {
+    display: none;
+  }
+  .gitako-code-fold-hidden {
+    display: table-cell;
+  }
+
+  .gitako-code-fold-attached {
+    tr {
+      .gitako-code-fold-handler {
+        display: initial;
+        position: absolute;
+        top: 0px;
+        right: 0px;
+        width: 20px;
+        height: 20px;
+        display: flex;
+        justify-content: center;
+        align-items: center;
+
+        &::before {
+          content: '';
+          display: block;
+          width: 10px;
+          height: 20px;
+          cursor: pointer;
+          user-select: none;
+          transition: 0.25s ease;
+          -webkit-mask-image: url('~@primer/octicons/build/svg/chevron-down.svg?inline');
+          mask-image: url('~@primer/octicons/build/svg/chevron-down.svg?inline');
+          -webkit-mask-size: contain;
+          mask-size: contain;
+          -webkit-mask-position: center;
+          mask-position: center;
+        }
+
+        @include interactive-background-on-before(
+          var(--gitako-icon-tertiary),
+          var(--gitako-icon-primary),
+          var(--gitako-icon-secondary)
+        );
+      }
+
+      &.active {
+        .gitako-code-fold-handler {
+          &::before {
+            transform: rotate(-90deg);
+          }
+
+          @include interactive-background-on-before(
+            var(--gitako-icon-secondary),
+            var(--gitako-icon-tertiary),
+            var(--gitako-icon-primary)
+          );
+        }
+      }
+    }
+
+    .gitako-code-fold-hidden {
+      display: none;
+    }
+  }
+  // code folding end
+
+  // clippy button
+  .markdown-body {
+    .clippy-wrapper {
+      position: relative;
+      width: 0;
+      height: 0;
+      top: 8px;
+      left: calc(100% - 40px);
+      z-index: 1;
+
+      .clippy {
+        width: 32px;
+        height: 32px;
+        border: 1px solid var(--gitako-border-tertiary);
+        border-radius: 4px;
+
+        @include interactive-background(
+          var(--gitako-btn-bg),
+          var(--gitako-btn-hover-bg),
+          var(--gitako-btn-focus-bg)
+        );
+        .icon {
+          width: 100%;
+          height: 100%;
+          display: block;
+          background-image: url('~@primer/octicons-react/build/svg/clippy-16.svg?inline');
+          background-position: center;
+          background-repeat: no-repeat;
+          &.success {
+            background-image: url('~@primer/octicons-react/build/svg/check-16.svg?inline');
+          }
+          &.fail {
+            background-image: url('~@primer/octicons-react/build/svg/x-16.svg?inline');
+          }
+        }
+      }
+    }
+  }
+
   // gitee
   &.git-project {
     #git-header-nav {
@@ -97,45 +235,6 @@ $minimal-z-index: max($github-header-z-index, $github-pull-request-float-header-
   }
 }
 
-.markdown-body {
-  .clippy-wrapper {
-    position: relative;
-    width: 0;
-    height: 0;
-    top: 8px;
-    left: calc(100% - 40px);
-    z-index: 1;
-
-    .clippy {
-      width: 32px;
-      height: 32px;
-      border: 1px solid var(--gitako-border-tertiary);
-      border-radius: 4px;
-      background: var(--gitako-bg-secondary);
-      &:hover {
-        background: var(--gitako-bg-secondary);
-      }
-      &:active {
-        background: var(--gitako-bg-secondary);
-      }
-      .icon {
-        width: 100%;
-        height: 100%;
-        display: block;
-        background-image: url('~@primer/octicons-react/build/svg/clippy-16.svg?inline');
-        background-position: center;
-        background-repeat: no-repeat;
-        &.success {
-          background-image: url('~@primer/octicons-react/build/svg/check-16.svg?inline');
-        }
-        &.fail {
-          background-image: url('~@primer/octicons-react/build/svg/x-16.svg?inline');
-        }
-      }
-    }
-  }
-}
-
 .progress-pjax-loader.is-loading {
   left: 0; /* reposition progress bar of GitHub */
 }
@@ -154,17 +253,13 @@ $minimal-z-index: max($github-header-z-index, $github-pull-request-float-header-
   @include flex-center();
   cursor: pointer;
   padding: 0;
-}
-
-@mixin button-color {
   border: none;
-  background: transparent;
-  &:hover {
-    background: var(--gitako-btn-hover-bg);
-  }
-  &:active {
-    background: var(--gitako-btn-focus-bg);
-  }
+
+  @include interactive-background(
+    transparent,
+    var(--gitako-btn-hover-bg),
+    var(--gitako-btn-focus-bg)
+  );
 }
 
 // Why does not TextInput get theme properly?
@@ -354,7 +449,6 @@ $minimal-z-index: max($github-header-z-index, $github-pull-request-float-header-
 
       .close-side-bar-button {
         @include icon-button;
-        @include button-color;
         width: $button-size;
         height: $button-size;
         border-radius: $button-size;
@@ -493,25 +587,23 @@ $minimal-z-index: max($github-header-z-index, $github-pull-request-float-header-
             align-items: center;
             padding: 0 4px;
 
-            .toggle-mode {
+            .toggle-search-mode {
               margin: 0;
               padding: 2px 4px;
               min-width: 32px;
               border: 1px solid var(--gitako-border-secondary);
               border-radius: 8px;
-              background: var(--gitako-bg-primary);
               color: var(--gitako-text-secondary);
               font-size: 12px;
               font-weight: 500;
               line-height: 1;
               outline: none;
-              &:focus,
-              &:hover {
-                background: var(--gitako-bg-secondary);
-              }
-              &:active {
-                background: var(--gitako-bg-tertiary);
-              }
+
+              @include interactive-background(
+                var(--gitako-bg-primary),
+                var(--gitako-bg-secondary),
+                var(--gitako-bg-tertiary)
+              );
             }
           }
         }
@@ -523,20 +615,22 @@ $minimal-z-index: max($github-header-z-index, $github-pull-request-float-header-
         }
 
         .node-item {
-          background: var(--gitako-bg-primary);
           &:hover {
             text-decoration: initial; // revert underline from .gitako-side-bar a:hover
             .node-item-label {
               text-decoration: underline; // apply underline like .gitako-side-bar a:hover
             }
           }
-          &.focused,
-          &:hover {
+
+          &.focused {
             background: var(--gitako-bg-tertiary);
           }
-          &:active {
-            background: var(--gitako-bg-secondary);
-          }
+
+          @include interactive-background(
+            var(--gitako-bg-primary),
+            var(--gitako-bg-secondary),
+            var(--gitako-bg-tertiary)
+          );
 
           &.disabled {
             pointer-events: none;
@@ -618,7 +712,6 @@ $minimal-z-index: max($github-header-z-index, $github-pull-request-float-header-
           .go-to-button,
           .find-in-folder-button {
             @include icon-button();
-            @include button-color();
             width: 28px;
             height: 28px;
             border-radius: 28px;
@@ -758,7 +851,6 @@ $minimal-z-index: max($github-header-z-index, $github-pull-request-float-header-
 
         .settings-button {
           @include icon-button();
-          @include button-color();
           $size: 32px;
           width: $size;
           height: $size;
diff --git a/src/utils/config/helper.ts b/src/utils/config/helper.ts
index 2bacbcf..20e2960 100644
--- a/src/utils/config/helper.ts
+++ b/src/utils/config/helper.ts
@@ -18,6 +18,7 @@ export type Config = {
   searchMode: SearchMode
   sidebarToggleMode: 'persistent' | 'float'
   commentToggle: boolean
+  codeFolding: boolean
 }
 
 enum configKeys {
@@ -35,6 +36,7 @@ enum configKeys {
   searchMode = 'searchMode',
   sidebarToggleMode = 'sidebarToggleMode',
   commentToggle = 'commentToggle',
+  codeFolding = 'codeFolding',
 }
 
 export const defaultConfigs: Config = {
@@ -52,6 +54,7 @@ export const defaultConfigs: Config = {
   searchMode: 'fuzzy',
   sidebarToggleMode: 'float',
   commentToggle: true,
+  codeFolding: true,
 }
 
 const configKeyArray = Object.values(configKeys)