Tweak the CSS of the TOC sidebar

assets/sass/layout.scss

@@ -26,37 +26,6 @@ body {
   overflow: visible;
 }
 
-aside {
-  width: 218px;
-  margin-bottom: 35px;
-  position: sticky;
-  top: 0;
-  max-height: 100vh;
-  overflow-y: auto;
-  /* align with the top of the content */
-  padding-top: 46px;
-}
-
-#toc {
-  border: 1px solid var(--main-border);
-  padding: .5em;
-  margin-top: 1rem;
-  border-top: 1px solid var(--main-border);
-  background: var(--sidebar-toc-bg-color);
-  margin-right: 0.5rem;
-}
-
-#toc ul {
-  list-style-type: square;
-}
-
-#toc li {
-  /* use margin instead of line height for spacing because sometimes the
-     headings wrap onto multiple lines */
-  line-height: 1.2em;
-  margin: 6px 0;
-}
-
 #content {
   width: 702px;
 }
@@ -157,47 +126,6 @@ header {
   }
 }
 
-// Navigation
-aside nav ul {
-  margin-bottom: 1.4em;
-  margin-left: 0;
-  font-size: 16px;
-  font-weight: bold;
-  list-style: none;
-
-  li {
-    margin-bottom: 0.5em;
-
-    a {
-      color: var(--nav-link-color);
-
-      &.active, &:hover {
-        color: var(--orange);
-      }
-    }
-
-    ul {
-      display: none;
-      margin-top: 0.3em;
-      margin-left: 20px;
-      font-size: 13px;
-      font-weight: normal;
-
-      li {
-        margin-bottom: 0;
-
-        a.active {
-          font-weight: bold;
-        }
-      }
-
-      &.expanded {
-        display: block;
-      }
-    }
-  }
-}
-
 .bottom-nav {
   @extend .callout;
   @include clearfix;

assets/sass/sidebar.scss

@@ -9,11 +9,44 @@ hr.sidebar {
   @include background-image-2x($baseurl + "images/sidebar-divider", 218px, 12px);
 }
 
+aside {
+  width: 218px;
+  margin-bottom: 35px;
+  top: 0;
+  max-height: 100vh;
+  /* align with the top of the content */
+  padding-top: 46px;
+}
+
+#toc {
+  border: 1px solid var(--main-border);
+  padding: .5em;
+  margin: 0 -1px 0 0; /* eat the #main border */
+  border-right: none;
+  z-index: 100;
+  position: relative;
+  background: var(--main-bg);
+
+  summary {
+
+  }
+
+  ul {
+    list-style-type: square;
+
+    li {
+      /* use margin instead of line height for spacing because sometimes the
+         headings wrap onto multiple lines */
+      line-height: 1.2em;
+      margin: 6px 0;
+      font-size: 0.8em;
+    }
+  }
+}
+
 aside.sidebar {
-  font-size: 13px !important;
   line-height: $base-line-height * 0.75;
   p {
-    font-size: 13px !important;
     line-height: $base-line-height * 0.75;
   }
 
@@ -29,6 +62,48 @@ aside.sidebar {
     }
   }
 }
+
+// Navigation
+aside nav ul {
+  margin-bottom: 1.4em;
+  margin-left: 0;
+  font-size: 16px;
+  font-weight: bold;
+  list-style: none;
+
+  li {
+    margin-bottom: 0.5em;
+
+    a {
+      color: var(--nav-link-color);
+
+      &.active, &:hover {
+        color: var(--orange);
+      }
+    }
+
+    ul {
+      display: none;
+      margin-top: 0.3em;
+      margin-left: 20px;
+      font-size: 13px;
+      font-weight: normal;
+
+      li {
+        margin-bottom: 0;
+
+        a.active {
+          font-weight: bold;
+        }
+      }
+
+      &.expanded {
+        display: block;
+      }
+    }
+  }
+}
+
 // Floating sidebar button for tablet and smaller screens
 aside.sidebar.active {
     @include responsive-sidebar-ui;
@@ -37,6 +112,11 @@ aside.sidebar.active {
   display: none;
 }
 
+aside details,
+aside nav {
+  padding: 0 1.5em;
+}
+
 // Breakpoint ----------------
 @media (max-width: $default) {
   .sidebar-btn {

layouts/partials/sidebar.html

@@ -49,40 +49,40 @@
         <a href="{{ relURL "community" }}"{{ if (eq $section "community") }} class="active"{{ end }}>Community</a>
       </li>
     </ul>
+  </nav>
 
-    {{ $headings := .Params.headings }}
-    {{ if $headings }}
-    <ul id="toc">
-      <li> Table of Contents
-        <ul class="expanded">
-          {{ range $i, $item := $headings }}
-            <li><a href="#{{ .id }}">{{ .text }}</a> </li>
-          {{ end }}
-        </ul>
-      </li>
-    </ul>
-    {{ end }}
+  {{ $headings := .Params.headings }}
+  {{ if $headings }}
+  <details id="toc" open>
+    <summary>Table of Contents</summary>
+    <ul>
+        {{ range $i, $item := $headings }}
+          <li><a href="#{{ .id }}">{{ .text }}</a> </li>
+        {{ end }}
+      </ul>
+    </li>
+  </details>
+  {{ end }}
 
-    {{ if (eq .Params.Sidebar "book") }}
-      <hr class="sidebar">
-      {{- /* If this page displays a section of the ProGit book, map all the translations thereof */ -}}
-      {{ with $.Page.Params.book }}
-        {{ $cs_number := .section.cs_number }}
-        {{ range $.Page.Site.Data.book }}
-          {{ $language_code := .language_code }}
-          {{ range .chapters }}
-            {{ range .sections }}
-              {{ if (eq .cs_number $cs_number) }}
-                {{ $.Scratch.SetInMap "translations" $language_code .url }}
-              {{ end }}
+  {{ if (eq .Params.Sidebar "book") }}
+    <hr class="sidebar">
+    {{- /* If this page displays a section of the ProGit book, map all the translations thereof */ -}}
+    {{ with $.Page.Params.book }}
+      {{ $cs_number := .section.cs_number }}
+      {{ range $.Page.Site.Data.book }}
+        {{ $language_code := .language_code }}
+        {{ range .chapters }}
+          {{ range .sections }}
+            {{ if (eq .cs_number $cs_number) }}
+              {{ $.Scratch.SetInMap "translations" $language_code .url }}
             {{ end }}
           {{ end }}
         {{ end }}
       {{ end }}
-      {{ partial "translations.html" . }}
-    {{ else if (and (ne $section "documentation") (ne $section "site")) }}
-      <hr class="sidebar">
-      {{ partial "book.html" }}
     {{ end }}
-  </nav>
+    {{ partial "translations.html" . }}
+  {{ else if (and (ne $section "documentation") (ne $section "site")) }}
+    <hr class="sidebar">
+    {{ partial "book.html" }}
+  {{ end }}
 </aside>