#59960 - Replace em-based line-height with unitless values in CSS

[andbalashov]

This commit addresses ticket #59960, which identified issues with em-based line-height values in various CSS files within the WordPress Administration interface. Following the suggestion in the ticket, the em-based line-heights are replaced with unitless values while keeping their numeric value the same.

This change primarily affects the 'common.css' file but also includes updates in 'edit.css', 'install.css', 'list-tables.css', 'media.css', 'nav-menus.css', and the Thickbox styles. The update aims to enhance the consistency and scalability of the CSS and resolve issues particularly noted in iframe-based editors.

Referencing the follow-up to ticket #44643, this update aligns with the focus on coding standards and CSS improvements within the WordPress administration environment. By making line-heights unitless, we ensure better adaptability across different font sizes and display environments.

Files updated:

• wp-admin/css/common.css
• wp-admin/css/edit.css
• wp-admin/css/install.css
• wp-admin/css/list-tables.css
• wp-admin/css/media.css
• wp-admin/css/nav-menus.css
• Compiled Thickbox styles (thickbox.css)

Trac ticket: https://core.trac.wordpress.org/ticket/59960

---

This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[mukeshpanchal27]

Thanks @andbalashov for the PR. The changes look good to me.

@sabernhardt could you please review it so we mark this ready for commit

[sabernhardt]

Thanks for creating a patch!

I have not checked all of these elements, but the popular-tags probably should keep the em unit.

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

Core Committers: Use this line as a base for the props when committing in SVN:

Props andbalashov, mukesh27, sabernhardt.

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[github-actions]

Test using WordPress Playground

The changes in this pull request can previewed and tested using a WordPress Playground instance.

WordPress Playground is an experimental project that creates a full WordPress instance entirely within the browser.

Some things to be aware of

• The Plugin and Theme Directories cannot be accessed within Playground.
• All changes will be lost when closing a tab with a Playground instance.
• All changes will be lost when refreshing the page.
• A fresh instance is created each time the link below is clicked.
• Every time this pull request is updated, a new ZIP file containing all changes is created. If changes are not reflected in the Playground instance,
  it's possible that the most recent build failed, or has not completed. Check the list of workflow runs to be sure.

For more details about these limitations and more, check out the Limitations page in the WordPress Playground documentation.

Test this pull request with WordPress Playground.