Please help us help you and fill where relevant:
Your LimeSurvey version:  LimeSurvey Cloud
Versió 5.6.41
Own server or LimeSurvey hosting:
Survey theme/template:
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Hi,
I'm trying to disable the question help text in all the questions in a survey with this code:

.questionhelp {
    display: none;
}

But I don't know where to include it in this specific survey in order to do it.

Thank you!

Extend your survey theme and add it to the custom.css file.