A Jekyll theme for lecture notes. Has light and dark color themes. Based on Minima. Works as remote theme for GitHub Pages.

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Jekyll theme for lecture notes

This Jekyll theme was devloped for one of my courses (web technology), you can view the course (and thus this theme) here. Jekyll is a static site generator that can be used to customize ones' GitHub Pages. The themes is set up with code-heavy teaching materials in mind.

This Jekyll theme is built on top of Minima, Jekyll's default theme. Only the necessary files were kept, the rest was stripped from the repo.

It should be possible to develop the lecture materials entirely in markdown, without regard for the cse-theme.

Spoilers, highlighting, note-taking and timing of active reading are built into the theme. All information is stored in the browser's localStorage.

Your repo should have the following files and folders in the root folder:

  • folders: _lectures, _practicals, _extras
  • files: index.md, 404.html, _config.yml

Important: when you make changes to the configuration file (e.g. trying out a new header image) it may look like these changes are not reflected on your site, even a few minutes after updating the configurations on GitHub. If you experience this, try to open the site in a private browser window! Depending on the browser, agressive caching may be employed and although the css/image/js files have changed on the server, the browser simply looks up cached versions of these files.

Table of Contents


This repository does not have to be forked or cloned. It can be used as remote theme. All that is needed in the repository to apply the theme to is to copy _config.yml and 404.html to your repository's root directory and add the following two lines to _config.yml:

baseurl: "/your-repository-name/"
remote_theme: chauff/cse-theme

The baseurl is used to set the root of the website (minus the hostname). The remote_theme has the format GITHUBUSERNAME/REPO and should be left as-is, unless the cse-theme repo was forked. That's it. Once the _config.yml file is added to the repository of choice this Jekyll theme will apply to it.

Customization happens via settings in _config.yml

This section walks through the site-wide options that can be set in the _config.yml file.

Course title and tagline

The browser (tab) title is set via tabTitle.

Three taglines can be set, which differ in size/coloring and whether they are animated.

  • line1Title: e.g. the course code (not animated)
  • line2Title: e.g. what this course is about in 1-2 terms (not animated; first letter of each term is given a different highlight)
  • line3Title: e.g. what this course is about in more detail (this line is animated and appears being typed out one letter at a time - unless you view the transcript in Safari which doesn't implement this particular CSS feature)

You can also opt to not set one or more of the titles, in this case remove the variable from _config.yml.

Color themes

Set the color theme (cssTheme), either light-green, light-grey, light-pink, or light-red.

Code color theme

Set the code color theme (cssCodeTheme), prepackaged are monokai, dracula, cobalt (dark background color) and perldoc (light background color).

Header image

Set the header image (headerImage). Included already are two variants, ../images/tudelft_ewi.jpg shows TU Delft's iconic EWI building and ../images/tudelft_ewi_bw.jpg is its grayscale variant.

Important: if you are using your own header image, the easiest option is to use an absolute URL (starting with http:// or https://). If you are using a relative URL, you need to keep track of the folder structure: for instance, you may want to create a folder images in your repository and add your header/footer images there. Then, headerImage should be set to ../../images/your-image.png as per the theme, the CSS file that contains the rule to load the header image is in assets/css/skin.css. Thus, two directories have to be traversed to reach a directory that is in your repository's root folder.

The best way to figure out what went wrong with your relative URL setting is to use your browser's Inspect element option to determine the absolute path that was derived from your relative URL. Below is a screenshot of what to look out for (using Firefox) when inspecting the <header> holding the background image:

Set the footer image (footerImage). Included already is a typical Dutch scene (by day and by night). The imagery has been created by David Maxwell!

The daytime image goes well with a light theme:

The night-time image goes well with a dark theme:

Important: the note above about absolute vs. relative URLs holds here as well.


Decide whether to show a warning of some type. If yes, set the warning string. This is one global warning string for the site. Whether or not a particular page shows the warning is determined by setting warning: true in each individual page's front matter (explained below in more detail). My standard use case is the updating of lecture materials throughout the year. Each page that has not been updated yet for the new year contains the warning. The warning appears just above the start of the page's content:

Small navigation bar

If a transcript is very long, switching to the next transcript can require a lot of scrolling (to scroll up and view the navigation bar again). For this reason the setting smallNavbar: true adds a small icon at the bottom left of the screen that pops up a small semi-transparent navigation pane when hovering over the icon with the mouse. It has the same structure/content as the original navigation bar.

The screenshots above were all made with the setting smallNavbar: false.

Here is how the icon looks like when the mouse does not hover over it:

And here is the mouse hovering over the icon:

Time spent (or: active reading)

In order to provide some feedback on the amount of time spent on each transcript, the following setting is available:

timeSpent: true
idleTimeout: 60

If timeSpent: true is set, a second icon appears next to the small navigation icon with a clock (as seen in the two screenshots above). Hovering over it reveals the amount of time spent on the particular page:

The idleTimeout setting is the number of seconds of idling that is required for the timer to stop. By default, this is 60 seconds. Idling occurs when (1) the page is not in focus or (2) the page is in focus but no mouse/keyboard/scroll activity is detected.

This is only a crude approximation of time spent on each transcript of course. It provides nothing more than an indication.

The timer information is stored in the browser's localStorage.


The design has basic responsiveness, it looks decent across large screens, tablets and phones.

Course content

This section describes how to set up the course content for this specific theme. Instead of starting from scratch, you can copy the respective files and folders from here: they have been included to make development of the theme easier.

Course information

The course information (overview, instructors, grading, etc.) should all be contained in index.md.

Adding a lecture

Place the lectures (each one in a separate markdown file) in the _lectures folder and add the YAML front matter at the top of each file, separated by tripple dashes:

layout: default
permalink: /http/
linkname: HTTP
ordering: 4
warning: true

The layout variable is always default in our case (other Jekyll themes may have different types of pages depending on the content type).

The permalink variable beautifies the URL (instead of just going with the filename, which may be rather ugly) and the linkname variable determines how the link appears in the navigation bar of the site.

As lectures are typically in a specific order, the ordering variable (just use integers, ascending order) determines the order of the lectures. Without this explicit ordering, the links would show up in alphabetic order.

Lastly, setting the warning variable to true ensures that there will be a warning box shown at the top of the page (removing the variable or another setting yields no warning box). The warning string itself should be set in _config.yml. Note that the div sizing and resizing based on the viewport size was hardcoded based on my typical update warning string -- significantly longer/shorter update strings may look odd or even overflow the div.

Note: all content appearing after the front matter is pushed into the content attribute, accessed as {{content}} in default.html.

Finally, we note that if you want to include a piece of text in a lecture which is the same for a number of lectures, it makes sense to move that text into a separate .md file (without a preamble). A typical use case may be an explanation of a set of icons or an indication of which materials are relevant for the exam or ... If we assume that this file is called explanation.md, the following line would copy the contents of that file into our lecture:

{% include_relative explanation.md %}

Adding practicals

Practicals (assignments, exercises, old exams, etc.) are added to the _practicals folder. The front matter is the same as for the lectures.

Source code

Source code can be written with the standard Markdown code markers:

source code goes here

Figure captions

There is no separate tag for figure captions in Markdown. The current regime is to use <sup>My caption.</sup> (note the extra empty line) :point_down::

![caniuse indexedb](/img/caniuse-indexedb.png)

<sup>Screenshot taken on September 3, 2020.</sup>

The result looks like this:

Debug information

To set debug information visually apart (separate background color and Debug on the sidebar) from the main text, use:

<debug-info markdown="block">add some debug information here.</debug-info>

The attribute markdown ensures that the Markdown inside this tag is parsed by the kramdown parser. If no Markdown is used for the text inside these tags, this attribute does not have to be set. This is a custom HTML element. The definition of the element can be found here.

Optional content

To set optional information visually apart (separate background color and Optional on the sidebar; different colors than the debug box) from the main text use:

<optional-info markdown="block">add some *optional* information here.</optional-info>

This is another custom HTML element. The definition of the element can be found here.


Spoilers are pieces of text that should only be visible once the mouse hovers over them. They can be added with a bit of HTML :point_down::

<spoiler-info markdown="block"> This is the spoiler text ... </spoiler-info>

This is another custom HTML element. The definition of the element can be found here.

Terminal recordings

For programming-heavy courses it can be useful to show terminal session recordings (e.g. to showcase how to run a script). Instead of creating a gif or showing a screencast of the terminal, it is possible to create recordings with asciinema.

These recordings are just plain text files and can be dropped into a folder (e.g. /cast) in your GitHub repository. To include the recordings in the transcript use:

<asciinema-player src="../cast/screen-recording-file.cast"></asciinema-player>

Questions and answers

To add a set of questions/answers (e.g. at the end of a transcript as self-check questions), the <details>/<summary> tag combination works well :point_down::

  <summary>What does JavaScript's hoisting principle refer to?</summary>
  Declarations are processed before any code is executed.

Note that the <details> tag does clash with how markdown handles code snippets. Code snippets are marked by backticks and rendered in a specific way; inside the <details> tag though this does not happen, the text is treated as normal text. The solution to this problem looks ugly but it works: whenever code is used inform the kramdown parser that this particular part of HTML contains Markdown to be parsed. For blocks of code, surround the code with <div markdown="1">..</div>. For elements that are part of the flow of the text, use <span markdown="span">11</span> instead:

    What will be the result of executing the above piece of JavaScript in the
    <div markdown="1">
      for (var i = 1; i <= 10; i++) { setTimeout(function () {
      console.log(i); }, 1000); }
  The answer is <span markdown="span">`11`</span>

The use of the markdown attribute here looks different to the use on the custom tags - this is not desired but the only way to have been found to work in practice. Why is this not a custom element? Because this tag combination comes with a set of default behaviours that are a good fit for questions.

Other information

The following sections are not necessary to know, but they may be useful if you want to develop the theme further or do a bit more than just adding transcripts.

Adding additional (analytics) scripts/content

To track for instance site visits, add a folder _extras: any file in this folder will be included right before the </body> tag in the default layout page. For the file content to be included, the file needs to start with an empty frontmatter. As an example, the statcounter snippet (which allows you to track site visits once you set up your own account) looks as follows:

<!-- Default Statcounter code  -->
<script type="text/javascript">
var sc_project = xxx;
var sc_invisible = 1;
var sc_security = "xxx";
<script type="text/javascript" src="https://www.statcounter.com/counter/counter.js" async></script>
<!-- End of Statcounter Code -->

CSS split

The CSS is split across a number of files:

  • /assets/css/skin.css contains the CSS for the layout of the entire page (CSS grid) and the header, navbar and footer.
  • /assets/css/github-markdown.css contains the CSS for the layout of the lectures/exercises, etc. The CSS comes from sindresorhus (with slight adaptations).
  • /assets/css/text-highlighting.css contains the CSS for the highlighting and note-taking features.

The color themes reside in /assets/css/themes/. To change the theme, go to _config.yml and change the cssTheme variable. The color theme of the page is separate from the color theme of the code snippets: these themes reside in /assets/css/themes/code. Change cssCodeTheme in _config.yml if you want to switch to another code highlighter. Code highlighter CSS files have to be compatible with pygments.

How to develop the theme further

Clone this repository and in the root folder run bundle exec jekyll serve --watch. The watch flag ensures that the Jekyll site is rebuilt when a file changes. The console output should look something like this:

Configuration file: /Users/claudia/GitHub/cse-theme/_config.yml
            Source: /Users/claudia/GitHub/cse-theme
       Destination: /Users/claudia/GitHub/cse-theme/_site
 Incremental build: disabled. Enable with --incremental
                    done in 1.001 seconds.
 Auto-regeneration: enabled for '/Users/claudia/GitHub/cse-theme'
    Server address:
  Server running... press ctrl-c to stop.

The server address tells you which URL to open to view the theme in action.

Note, that changing the _config.yml file (e.g. to switch to a different css theme) requires a restart of the server.


GitHub Pages does not run the latest Jekyll version, make sure to check the right Jekyll version when looking at the documentation. GitHub's Jekyll version can be found here. For example, the very useful sort_by is a Jekyll 4 feature.

If you made changes to the configuration but don't see them reflected on the served pages, clear the browser's cache or try the private mode (Firefox likes caching a lot ...).

The table of contents for each transcript can be easily generated with VS Code's Markdown all in one extension. In general, writing your Markdown in VSC is a nice way of doing things!

If screenshots of code snippets are needed (e.g. for slides), head to Carbon for high-resolution images.

Inside VS Code, CodeSnap works well, the only problem is that the images produced are of low resolution. Maybe this will be fixed soon ...

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