What is a Theme Style Kit
A Theme Style Kit is a saved configuration of Elementor Theme Styles. Think of it as a Theme Style Preset, that holds all the design information of your layout.
Style Kits plugin adds a number of useful UI controls to the Elementor Theme Styles panel, that allows you to control more design attributes from within the Theme Style panel, including:
Style Kits Pro adds even more UI controls in the Theme Styles Panel, giving you more design flexibility when working with global styles.
Applying Theme Style Kits on specific pages
Although it is suggested to use a global theme Style Kit in your site, you can choose to apply any of your available Style Kits on a specific page. This can be done by navigating to the Page Settings, and opening the Style Kits panel as the screenshot below shows.
If the page you are working on is already using the Global Theme Style Kit, then you will see the blue alert that says "You are editing the Global Style Kit", and the dropdown will already be populated with the Style Kit that has been set as Global.
However, you can override the Global Theme Style Kit for this page, by choosing any of your other available Style Kits.