The correct option is Javascript.

The feedback widget runs in the visitor's browser and a custom trigger must be implemented client side so it can listen for user actions and call the widget API. That interactive behavior is implemented with Javascript, which is why Javascript is required for a custom trigger.

HTML defines the structure of the page and can host the widget markup but it cannot implement the interactive logic needed for a custom trigger, so it is not the correct choice.

JQL is a query language for searching Jira issues and it does not provide client side scripting capabilities, so it cannot be used to implement a trigger.

CSS controls presentation and styling and it cannot execute logic or handle events required to open the widget, so it is not suitable for a custom trigger.

Java runs on the server or in a different runtime than the browser and it is not the language used to implement in page widget triggers, so it is not the required language.

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