Astra < 4.12.4 - Contributor+ Stored XSS via Post Meta

Description

The theme is vulnerable to Stored Cross-Site Scripting via the `ast-page-background-meta` and `ast-content-background-meta` post meta fields due to insufficient input sanitization on meta registration and missing output escaping in the `astra_get_responsive_background_obj()` function for four CSS-context sub-properties (`background-color`, `background-image`, `overlay-color`, `overlay-gradient`). This makes it possible for authenticated attackers, with Contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.