added ability to collapse headers

_plugins/details.rb

+# _plugins/details_tag.rb -- copied from http://movb.de/jekyll-details-support.html
+
+module Jekyll
+  module Tags
+    class DetailsTag < Liquid::Block
+
+      def initialize(tag_name, markup, tokens)
+        super
+        @caption = markup
+      end
+
+      def render(context)
+        site = context.registers[:site]
+        converter = site.find_converter_instance(::Jekyll::Converters::Markdown)
+        # below Jekyll 3.x use this:
+        # converter = site.getConverterImpl(::Jekyll::Converters::Markdown)
+        caption = converter.convert(@caption).gsub(/<\/?p[^>]*>/, '').chomp
+        body = converter.convert(super(context))
+        "<details><summary>#{caption}</summary>#{body}</details>"
+      end
+
+    end
+  end
+end
+
+Liquid::Template.register_tag('details', Jekyll::Tags::DetailsTag)

assets/css/style.scss

@@ -13,9 +13,22 @@ $lab-background:#d8e6c9;
 $background: #d8e6c9;
 $highlight-dark: red;
 $highlight-light: lightcoral;
+$break-color: #ddeeee;
+$activity-color:   #f0f4f2;
 $highlight-darkest: #660000;
 $white: white;
 
+details {
+    summary {
+	font-weight:bold;
+	font-size: large;
+	background-color:   $background;
+	color: $dark-color;
+	padding:5px;
+    }
+    padding:1em;
+}
+
 a {
     color: $link-color;
 }
@@ -115,6 +128,41 @@ dl dt.lecture {
     margin-top: 1em !important;
 }
 
+dl dt.homework {
+    &::before {
+            font-family: FontAwesome;
+            font-size: 1.2em;
+            content: "\e066";
+            float: left;
+            margin-right: 0.4em;
+        }
+    style:bold;
+    font-size: large;
+    background-color:   $activity-color;
+    color: $dark-color;
+    padding:5px;
+    margin-top: 1em !important;
+    margin-left: 1em !important;
+}
+
+dl dt.activity {
+    style:bold;
+    font-size: large;
+    background-color:   $activity-color;
+    color: $dark-color;
+    padding:5px;
+    margin-top: 1em !important;
+}
+
+dl dt.break {
+    style:bold;
+    font-size: large;
+    background-color:   $break-color;
+    color: $dark-color;
+    padding:5px;
+    margin-top: 1em !important;
+}
+
 dl dt.demonstration {
     style:bold;
     font-size: large;