Right Side Bar adjustment

Hi,
I have the following problem:
Whenever there are no widgets assigned to the sidebar the archive, categories and calendar widget seem to be shown as default, eventhough I created no widgets. I turned them off with the css code:

.widget_calendar {
display: none;
}

.widget_archive {
display: none;
}

.widget_categories {
display: none;
}

This works fine, but leaves the spot where the sidebar is empty. The main content is cropped to the left side of the screen. How can I use the full width of the screen without any sidebar widgets?

Thanks in advance.

Best,
Stephan

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