Convert discussion block sass variable into css variables

[salman2013]

Description:

In this PR i converted builtin discussion block Sass variables into CSS variables.

I added them all inside :root { ... } in file: common/static/sass/_builtin-block-variables.scss
(CSS var reference on MDN)

Following is the list of variables:

$actions-dropdown-width
$actions-dropdown-offset
$border-color-4
$comment-image-dimension
$forum-color-active-thread
$forum-color-hover
$forum-color-active-text
$forum-color-background
$forum-x-large-font-size
$forum-color-copy-light
$forum-large-font-size
$forum-border-radius
$forum-base-font-size
$forum-small-font-size
$forum-color-border
$forum-color-background-light
$forum-color-editor-preview-label
$forum-color-following
$forum-color-error
$forum-color-pinned
$forum-color-reported
$forum-color-closed
$forum-color-staff
$forum-color-community-ta
$forum-color-response-count
$forum-color-read-post
$forum-color-hover-thread
$forum-color-reading-thread
$forum-color-never-read-post
$forum-color-navigation-bar
$forum-color-primary
$green
$line-height-base
$pink
$post-image-dimension
$response-image-dimension
$serif

Ticket Ref: openedx/public-engineering#456

Acceptance Criteria

The Discussion XBlock UI should remain unaffected.

How to test:

• Run npm run compile-sass-dev in lms shell.
• Open discussion XBlock in the lms. (To enable discussion block we can follow Discussion Block Extraction #36539 (comment))
• In dev tool We can use following command in console to verify the above mentioned variables

getComputedStyle(document.documentElement).getPropertyValue('--actions-dropdown-width')

Testing results

[openedx-webhooks]

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[farhan]

$container-max-widths

is used here, shouldn't it be converted?

[salman2013]

$container-max-widths

is used here, shouldn't it be converted?

Yes i believe it should be converted so i added this into _builtin-block-variables file and used the converted one.

[farhan]

Seems good to me