The Magento UI library
The Magento UI library was created so that the developers of Magento themes could use a ready and optimized solution that supported the development of new Magento themes. The library is based on the LESS preprocessor, which facilitates the implementation of customizations in Magento 2 theme development.
The Magento UI library provides the following elements and properties so that theme developers can customize the user interface of their projects:
actions-toolbar: Includes a set of actions on a page, such as submit buttons and links to navigate the page
breadcrumbs: Allows users to keep track of their location within the website
buttons: A set of different buttons to use in your project
dropdowns: A set of drop-downs to use in your project
forms: Customize your forms using the mixins and by configuring the global variables
icons: Can be added to any HTML tag, and represented by fonts, images, or sprites
layout: Provides mixins for flexible page layout customization
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