An Adobe Commerce developer is customizing buttons for a custom theme that inherits Magento/blank theme and needs to override the default values. Where would the default values for the buttons be located?

The Adobe Commerce UI library contains the core LESS files that define the default styling for frontend components. These library files are located in the lib/web/css/source/lib/ directory. The specific file that holds the default variables and mixins for button styling is buttons.less. To customize buttons, a developer would override the variables or extend the styles defined in this file within their custom theme, which inherits from a parent theme like Magento/blank.

B. lib/web/less/source/lib/buttons.less: This path is incorrect. The standard directory for source LESS files in the core library is lib/web/css/source/, not lib/web/less/source/.
C. lib/web/css/source/lib/button.less: This path is incorrect due to the filename. The correct file is named with a plural, buttons.less, as it contains styles for various button states and types.

1. Adobe Commerce Developer Documentation, Frontend Developer Guide > Magento UI library: "The Magento UI library source files are located in /lib/web/css/." This section establishes the root directory for the UI library files. The specific path to the source library components is lib/web/css/source/lib/. (Reference: Adobe Commerce DevDocs, Frontend Developer Guide, Magento UI library).

2. Adobe Commerce Developer Documentation, Frontend Developer Guide > CSS in Magento: This document describes the file structure for CSS and LESS files. It confirms that core, non-module-specific LESS files, such as the UI library, reside in lib/web/css. The file lib/web/css/source/lib/buttons.less is the source for button mixins and variables. (Reference: Adobe Commerce DevDocs, Frontend Developer Guide, Cascading style sheets (CSS), CSS file locations).