Styling in edx-platform#

Over time, our Sass styling has become a little convoluted, with three major reworkings often leading to confusion when a developer needs to style in multiple locations across edx-platform. The main endeavors were v1, v2 (or pattern library) and Bootstrap. We are trying to move away from using v2, as the pattern library is deprecated, but there may still be locations in the code that reference those styles (please remove them as you see fit).

Our platform uses a system of Sass partials that combine to compile into a single large css file to be rendered on the page. From the Sass docs:

You can create partial Sass files that contain little snippets of CSS that you can include in other Sass files. This is a great way to modularize your CSS and help keep things easier to maintain. A partial is simply a Sass file named with a leading underscore. You might name it something like _partial.scss. The underscore lets Sass know that the file is only a partial file and that it should not be generated into a CSS file. Sass partials are used with the @import directive.

This structure allows us to break up our styling into small pieces, making readability and maintenance easier, while often at the expense of structural complexity as a code base grows. Here is an example, directly from edx-platform, for how the partials flow to a single scss file that compiles into CSS for the page to use. This is a page that uses v1 styling.

Sass Compilation for v1 CSS

Sass Compilation for v1 CSS#

Note that this only shows an example, there are far more partials that come together to make the lms-main-v1.css final file.

As you can see, the lms-main-v1.scss file does not have a leading underscore, telling the compilation to turn that scss file into an actual css file to be rendered on the page. If you were to use the Chrome Inspector tool and look at the styling, you will see that there is one unified lms- main-v1.css file that contains all the element styles.

The lms-main-v1.scss file uses the @import statement to pull in the _build- base-v1.scss and build-lms-v1.scss files which in turn import more partials down the road. It is critical to recognize that this tree works in a depth-first, first-come-first-serve manner. That means that styles that are imported early in the process cannot reference Sass variables imported later in the process (ie: bootstrap/variables cannot reference variables from shared/header).

This diagram describes the process for the v1 styles, and there is a similar setup for lms-main-v2.scss as well as bootstrap/lms-main.scss. Each individual HTML page on the edx-platform specifies which of the three that page wants to use for styling. Please note that as an organization, we are slowly trying to 1) move everything over to the bootstrap/lms-main.scss file and 2) deprecate and stop using any v2 files. lms-main-v1.scss can still be used, but a migration over to bootstrap/lms-main.scss, and a migration of any relevant partials from the v1 structure, would be a valuable endeavor.

Please note that as you add partials, make sure that they are not already being imported in another file (ie: you add a node to the tree above that already exists on the tree).

What theming does, and how to do it#

By thinking about the styling as a tree, theming becomes a lot simpler. All theming means is that you can override one of the partials above by matching the exact path in the edx-platform/themes directory. So, for example, to override the shared header file (located at lms/static/sass/shared/_header), you would simply go into the edx-platform/themes/[theme you want to override]/lms/static/shared folder and add a _header.scss file. When django compiles the assets, it will use this file as a replacement to the main edx-platform implementation.

If you look at the actual code base, you will see that we have a standard of using the partials directory for these overrides files. This keeps the specific components isolated from the core styling to reduce errors when people override files and forget to import other files that are needed elsewhere on the site. This is a good practice that future development should adhere to.

Final Note: When dealing with front end changes, it is a good idea to also check the edx-themes repo, that works exactly like our themes folder, but also includes html templates that can further confuse things.

Bootstrap and edx-platform#

In a month and a half endeavor in the Fall, Andy and I worked on integrating Bootstrap into the platform for three main reasons.

1. To unify our styling: By specifying colors and variables that can be used universally, reducing the ‘50 shades of grey’ issue and inconsistencies in the ways that we style components.

2. To add a widely used component library: Bootstrap has a robust community of developers that contribute to their open source component library, allowing for easier prototyping and create of front end experiences.

3. To simplify theming: Since we now have a single unified source of truth for our variables, openedx instances and alternative themes can simply override those files to customly style their sites.

Relating to the above styling conversation, we have pulled in the entire bootstrap styling library into lms-main.scss, but only partially pulled it into the v1 and v2 implementations due to naming conflicts. For example, we could not pull in the bootstrap modal, due to conflicts with our own modal styling (both use the generic .modal class). We were, however, able to pull in the entire bootstrap javascript file, since that file overrides jQuery in ways that our current application does not (meaning no conflicts).

Therefore, any pages that use lms-main.scss can use any bootstrap component out of the box. To use bootstrap components in older, v1, v2 pages we have to manually specify the exact Sass partial from the edx- platform/node_modules/bootstrap that we want. For example, to add an alert to a v1 page, you would add to base/build the partial bootstrap/scss/alert. Steps outlined below.

1. Determine from the node_modules/bootstrap/scss directory which component you want to import.

2. Add that import (i.e: bootstrap/scss/alert) somewhere in the Sass tree, most likely to base/build.scss

3. NOTE: Run paver compile_sass to make sure it works, if not, there is likely a bootstrap mixin that you are missing. If so, search for the mixin in node_modules/bootstrap/scss/mixins and import it (i.e: bootstrap/scss/mixins/alert)

4. You are done. Add the component using HTML or Javascript. Use the Bootstrap Component Docs for examples.


I want to add a new scss file for a feature on a particular page, how do I add it?#

First, you want to check which root file the page uses, whether it is lms-main-v1, lms-main-v2 or lms-main. Then, go to that file and trace down the tree to find a good spot for the new scss file to live. So, for example, if you are adding an LMS feature and the page uses lms-main-v1, you can trace down lms- main-v1 > _build_lms_v1 and see that there are plenty of standalone imports that look like features. Simply add your file to the lms/static/sass directory in a similar manner and add it as an @import to that page.

Why isn’t my bootstrap component styling like in the bootstrap docs?#

In any pages that use the lms-main.css compiled file, the bootstrap component will render. This case only arises when we are working with a legacy v1 or v2 page. As outlined earlier in this document, we cannot import the entire bootstrap repository due to conflicts with old styling. For v1 and v2, we are gradually pulling in styles for components, so this must mean that you are building a component that has not yet been used in the LMS/Studio.

To add the styles, you first need to find them in the bootstrap package. To do so, search at edx-platform/node_modules/bootstrap/scss for the file that you need. Then add this to the v1 or v2 tree, most likely to the build/base.scss file. Note that you may hit issues with mixins when you try to compile the SASS. In this case, check the edx-platform/node_modules/bootstrap/scss/mixins folder and import that into the lms or studio before trying to import the component styling.