zulip/docs/subsystems/html_css.md

HTML and CSS

Zulip CSS organization

The Zulip application's CSS can be found in the static/styles/ directory. Zulip uses Bootstrap as its main third-party CSS library.

Zulip currently does not use any CSS preprocessors, and is organized into several files. For most pages, the CSS is combined into a single CSS file by the static asset pipeline, controlled by the PIPELINE_CSS code in zproject/settings.py.

The CSS files are:

• portico.css - Main CSS for logged-out pages
• pygments.css - CSS for Python syntax highlighting
• activity.css - CSS for the activity app
• fonts.css - Fonts for text in the Zulip app
• static/third/thirdparty-fonts.css - Font Awesome (used for icons)

The CSS for the Zulip web application UI is primarily here:

• settings.css - CSS for the Zulip settings (including organization settings) pages
• zulip.css - CSS for the rest of the Zulip logged-in app
• media.css - CSS for media queries (particularly related to screen width)

We are in the process of splitting zulip.css into several more files; help with that project is very welcome!

Editing Zulip CSS

If you aren't experienced with doing web development and want to make CSS changes, we recommend reading the excellent Chrome web inspector guide on editing HTML/CSS, especially the section on CSS to learn about all the great tools that you can use to modify and test changes to CSS interactively in-browser (without even having the reload the page!).

CSS Style guidelines

Avoid duplicated code

Without care, it's easy for a web application to end up with thousands of lines of duplicated CSS code, which can make it very difficult to understand the current styling or modify it. We would very much like to avoid such a fate. So please make an effort to reuse existing styling, clean up now-unused CSS, etc., to keep things maintainable.

Be consistent with existing similar UI

Ideally, do this by reusing existing CSS declarations, so that any improvements we make to the styling can improve all similar UI elements.

Use clear, unique names for classes and object IDs

This makes it much easier to read the code and use git grep to find where a particular class is used.

Validating CSS

When changing any part of the Zulip CSS, it's important to check that the new CSS looks good at a wide range of screen widths, from very wide screen (e.g. 1920px) all the way down to narrow phone screens (e.g. 480px).

For complex changes, it's definitely worth testing in a few different browsers to make sure things look the same.