Option B is the correct way to initialize a widget using the data-mage-init attribute. The attribute value should be a JSON object with the widget name as the key and the widget options as the value. Option A is incorrect because it uses a string instead of an object for the attribute value. Option C is incorrect because it uses a colon instead of a comma to separate the widget name and the options.

To override the parent theme styles, the developer needs to change the web/css/source/_extend.less file in the child theme. This file is used to import and extend the parent theme styles without modifying the original files. The developer can use the @import directive to import the parent theme styles and then use the .lib-css() mixin to override the CSS properties. For example:

@import ‘source/_extend.less’; // Import parent theme styles .lib-css(color, red); // Override color property

The web/css/source/_extends.less and web/css/source/_theme.less files are not valid and will not work, as they do not follow the theme structure or the naming convention. References: [Theme inheritance], [Extend parent theme styles]

The best way to customize a template file from a third-party module is to create a new theme that inherits from the parent theme and override the template file in the app/design/frontend/Custom/Theme/Vendor_Module/templates directory. This way, the customization is isolated from the original module and can be applied to a specific website or store view. Creating another layout file or a new module would not be as simple or flexible as creating a new theme. References: Frontend development guide, [Create a theme], [Theme inheritance]