CSS line-height values should be unitless - buttons.css

[ianbelanger]

As outlined in #44643, CSS line-height values should be unitless unless necessary to be defined as a specific pixel value. It was suggested that we break up 44643 by stylesheet in order to better track them.

This ticket covers much of wp-includes/css/buttons.css, see patch notes below

Note: The patch was tested only on a Windows machine in Chrome, Firefox, IE11 and Edge. As per https://core.trac.wordpress.org/ticket/44643#comment:23 it should probably be tested on other OS's and supported browsers.

Patch Notes:

Unable to find selectors in the DOM. It appears that this particular selector no longer exists in core

line 360 - #media-upload.wp-core-ui .button

[mukesh27]

I tested attached patch successfully without any error in Ubuntu 18.04.2 LTS with Google Chrome Version 73.0.3683.75 and Firefox Version 65.0.1

[ianbelanger]

Updates patch with more precise line-height calculations

[SergeyBiryukov]

In 45476:

CSS Coding Standards: Use unitless values for line-height in wp-includes/css/buttons.css.

Props ianbelanger, pbiron, afercia.
Fixes #46526. See #44643.