Cross-site scripting(XSS) is a type of computer security vulnerability tipically found in Web application. XSS enables attackers to inject client-side scripts into Web pages viewed by other users. '@import' is used to include external css file in HTML file. Security problem will occur if used not carefully. This rule detects '@import' in HTTP request. This rule supports to defend the A3: Injection of OWASP Top 10 - 2021. Other reference:None