Dear @marjo483,
Thank you for the topic.
In order to achieve your desired result, please, first of all, go and find the Survey width option.
By this option, you can specify the width of the particular survey.
Here you can just leave the field blank and the system will automatically set 100% for the width.
In order to find this option, you can go to the Surveys > particular survey > Styles tab.
See the screenshot: https://ibb.co/tDz1WPD
Then, I want to mention, that we have created a Custom CSS special for you to achieve your preferred result.
Please insert this Custom CSS code into the Theme > Customize > Additional CSS.
#ays-survey-container-YOUR_SURVEY_ID{
margin: 0;
}
Please note, that it will take the max-width of your Theme Container.
Please check this and let us know about the outcome.
Thank you.