Merge branch 'docs-update-style-env-var' into 'master'

Doc: Update environment variables page with styling

See merge request gitlab-org/gitlab!44352

doc/administration/environment_variables.md

 ---
-stage: Verify
-group: Continuous Integration
+stage: Enablement
+group: Distribution
 info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
 type: reference
 ---
 
-# Environment Variables
+# Environment variables
 
 GitLab exposes certain environment variables which can be used to override
 their defaults values.
 
-People usually configure GitLab via `/etc/gitlab/gitlab.rb` for Omnibus
+People usually configure GitLab with `/etc/gitlab/gitlab.rb` for Omnibus
 installations, or `gitlab.yml` for installations from source.
 
-Below you will find the supported environment variables which you can use to
-override certain values.
+You can use the following environment variables to override certain values:
 
 ## Supported environment variables
 
-Variable | Type | Description
--------- | ---- | -----------
-`ENABLE_BOOTSNAP`                          | string  | Enables Bootsnap for speeding up initial Rails boot (`1` to enable)
-`GITLAB_CDN_HOST`                          | string  | Sets the base URL for a CDN to serve static assets (e.g. `//mycdnsubdomain.fictional-cdn.com`)
-`GITLAB_ROOT_PASSWORD`                     | string  | Sets the password for the `root` user on installation
-`GITLAB_HOST`                              | string  | The full URL of the GitLab server (including `http://` or `https://`)
-`RAILS_ENV`                                | string  | The Rails environment; can be one of `production`, `development`, `staging` or `test`
-`DATABASE_URL`                             | string  | The database URL; is of the form: `postgresql://localhost/blog_development`
-`GITLAB_EMAIL_FROM`                        | string  | The e-mail address used in the "From" field in e-mails sent by GitLab
-`GITLAB_EMAIL_DISPLAY_NAME`                | string  | The name used in the "From" field in e-mails sent by GitLab
-`GITLAB_EMAIL_REPLY_TO`                    | string  | The e-mail address used in the "Reply-To" field in e-mails sent by GitLab
-`GITLAB_EMAIL_SUBJECT_SUFFIX`              | string  | The e-mail subject suffix used in e-mails sent by GitLab
-`GITLAB_UNICORN_MEMORY_MIN`                | integer | The minimum memory threshold (in bytes) for the Unicorn worker killer
-`GITLAB_UNICORN_MEMORY_MAX`                | integer | The maximum memory threshold (in bytes) for the Unicorn worker killer
-`GITLAB_SHARED_RUNNERS_REGISTRATION_TOKEN` | string  | Sets the initial registration token used for runners
-`UNSTRUCTURED_RAILS_LOG`                   | string  | Enables the unstructured log in addition to JSON logs (defaults to `true`)
+| Variable                                   | Type    | Description                                                                                             |
+|--------------------------------------------|---------|---------------------------------------------------------------------------------------------------------|
+| `DATABASE_URL`                             | string  | The database URL; is of the form: `postgresql://localhost/blog_development`.                            |
+| `ENABLE_BOOTSNAP`                          | string  | Enables Bootsnap for speeding up initial Rails boot (`1` to enable).                                    |
+| `GITLAB_CDN_HOST`                          | string  | Sets the base URL for a CDN to serve static assets (for example, `//mycdnsubdomain.fictional-cdn.com`). |
+| `GITLAB_EMAIL_DISPLAY_NAME`                | string  | The name used in the **From** field in emails sent by GitLab.                                           |
+| `GITLAB_EMAIL_FROM`                        | string  | The email address used in the **From** field in emails sent by GitLab.                                  |
+| `GITLAB_EMAIL_REPLY_TO`                    | string  | The email address used in the **Reply-To** field in emails sent by GitLab.                              |
+| `GITLAB_EMAIL_SUBJECT_SUFFIX`              | string  | The email subject suffix used in emails sent by GitLab.                                                 |
+| `GITLAB_HOST`                              | string  | The full URL of the GitLab server (including `http://` or `https://`).                                  |
+| `GITLAB_ROOT_PASSWORD`                     | string  | Sets the password for the `root` user on installation.                                                  |
+| `GITLAB_SHARED_RUNNERS_REGISTRATION_TOKEN` | string  | Sets the initial registration token used for runners.                                                   |
+| `GITLAB_UNICORN_MEMORY_MAX`                | integer | The maximum memory threshold (in bytes) for the [unicorn-worker-killer](operations/unicorn.md#unicorn-worker-killer).      |
+| `GITLAB_UNICORN_MEMORY_MIN`                | integer | The minimum memory threshold (in bytes) for the [unicorn-worker-killer](operations/unicorn.md#unicorn-worker-killer).      |
+| `RAILS_ENV`                                | string  | The Rails environment; can be one of `production`, `development`, `staging`, or `test`.                 |
+| `UNSTRUCTURED_RAILS_LOG`                   | string  | Enables the unstructured log in addition to JSON logs (defaults to `true`).                             |
 
 ## Complete database variables
 
-The recommended way of specifying your database connection information is to set
-the `DATABASE_URL` environment variable. This variable only holds connection
-information (`adapter`, `database`, `username`, `password`, `host` and `port`),
-but not behavior information (`encoding`, `pool`). If you don't want to use
-`DATABASE_URL` and/or want to set database behavior information, you will have
-to either:
+The recommended method for specifying your database connection information is
+to set the `DATABASE_URL` environment variable. This variable contains
+connection information (`adapter`, `database`, `username`, `password`, `host`,
+and `port`), but no behavior information (`encoding` or `pool`). If you don't
+want to use `DATABASE_URL`, or want to set database behavior information,
+either:
 
-- copy our template file: `cp config/database.yml.env config/database.yml`, or
-- set a value for some `GITLAB_DATABASE_XXX` variables
+- Copy the template file, `cp config/database.yml.env config/database.yml`.
+- Set a value for some `GITLAB_DATABASE_XXX` variables.
 
 The list of `GITLAB_DATABASE_XXX` variables that you can set is:
 
-Variable | Default value | Overridden by `DATABASE_URL`?
--------- | ------------- | -----------------------------
-`GITLAB_DATABASE_ADAPTER`   | `postgresql`                          | Yes
-`GITLAB_DATABASE_DATABASE`  | `gitlab_#{ENV['RAILS_ENV']`           | Yes
-`GITLAB_DATABASE_USERNAME`  | `root`                                | Yes
-`GITLAB_DATABASE_PASSWORD`  | None                                  | Yes
-`GITLAB_DATABASE_HOST`      | `localhost`                           | Yes
-`GITLAB_DATABASE_PORT`      | `5432`                                | Yes
-`GITLAB_DATABASE_ENCODING`  | `unicode`                             | No
-`GITLAB_DATABASE_POOL`      | `10`                                  | No
+| Variable                    | Default value                  | Overridden by `DATABASE_URL`? |
+|-----------------------------|--------------------------------|-------------------------------|
+| `GITLAB_DATABASE_ADAPTER`   | `postgresql`                   | **{check-circle}** Yes        |
+| `GITLAB_DATABASE_DATABASE`  | `gitlab_#{ENV['RAILS_ENV']`    | **{check-circle}** Yes        |
+| `GITLAB_DATABASE_ENCODING`  | `unicode`                      | **{dotted-circle}** No        |
+| `GITLAB_DATABASE_HOST`      | `localhost`                    | **{check-circle}** Yes        |
+| `GITLAB_DATABASE_PASSWORD`  | _none_                         | **{check-circle}** Yes        |
+| `GITLAB_DATABASE_POOL`      | `10`                           | **{dotted-circle}** No        |
+| `GITLAB_DATABASE_PORT`      | `5432`                         | **{check-circle}** Yes        |
+| `GITLAB_DATABASE_USERNAME`  | `root`                         | **{check-circle}** Yes        |
 
 ## Adding more variables
 
-We welcome merge requests to make more settings configurable via variables.
-Please make changes in the `config/initializers/1_settings.rb` file and stick
-to the naming scheme `GITLAB_#{name in 1_settings.rb in upper case}`.
+We welcome merge requests to make more settings configurable by using variables.
+Make changes to the `config/initializers/1_settings.rb` file, and use the
+naming scheme `GITLAB_#{name in 1_settings.rb in upper case}`.
 
 ## Omnibus configuration
 
-To set environment variables, follow [these
-instructions](https://docs.gitlab.com/omnibus/settings/environment-variables.html).
+To set environment variables, follow [these instructions](https://docs.gitlab.com/omnibus/settings/environment-variables.html).
 
 It's possible to preconfigure the GitLab Docker image by adding the environment
 variable `GITLAB_OMNIBUS_CONFIG` to the `docker run` command.
-For more information see the [Pre-configure Docker container](https://docs.gitlab.com/omnibus/docker/#pre-configure-docker-container)
-section in the Omnibus documentation.
+For more information, see the [Pre-configure Docker container](https://docs.gitlab.com/omnibus/docker/#pre-configure-docker-container)
+section of the Omnibus GitLab documentation.