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. HTML tag '<style>' defines the css format of the webpage. Attackers can use '<style>' to implement XSS attack. This rule detects '<style>' in HTTP request. This rule supports to defend the A3: Injection of OWASP Top 10 - 2021. Other reference:None