Allow heading levels 1-6 in table of contents

Adjust minimum and maximum levels to allow all headings and fix CSS to style indentation and nested lists properly in jekyll-toc and Kramdown generated table of contents.

Fixes mmistakes#1782

Author: mmistakes

_layouts/single.html

@@ -38,7 +38,7 @@
           <aside class="sidebar__right {% if page.toc_sticky %}sticky{% endif %}">
             <nav class="toc">
               <header><h4 class="nav__title"><i class="fas fa-{{ page.toc_icon | default: 'file-alt' }}"></i> {{ page.toc_label | default: site.data.ui-text[site.locale].toc_label }}</h4></header>
-              {% include toc.html sanitize=true html=content h_min=2 h_max=3 class="toc__menu" %}
+              {% include toc.html sanitize=true html=content h_min=1 h_max=6 class="toc__menu" %}
             </nav>
           </aside>
         {% endif %}

_sass/minimal-mistakes/_navigation.scss

@@ -540,16 +540,23 @@
   }
 
   li ul > li a {
-    padding-left: 1.75rem;
+    padding-left: 1.5rem;
     font-weight: normal;
   }
 
-  /* hide sub sub links on small screens*/
-  li > ul li {
-    display: none;
+  li ul li ul > li a {
+    padding-left: 2rem;
+  }
 
-    @include breakpoint($medium) {
-      display: block;
-    }
+  li ul li ul li ul > li a {
+    padding-left: 2.5rem;
+  }
+
+  li ul li ul li ul li ul > li a {
+    padding-left: 3rem;
+  }
+
+  li ul li ul li ul li ul li ul > li a {
+    padding-left: 3.5rem
   }
 }