TYPO3 doesn't hide the Bootstrap hamburger menu after closing it

Question

I have a problem with my navigation in the mobile view. The menu works fine when it is open, but when I close it the whole menu moves next to the navigation bar.

Here is a pic of the problem:

Before:

Could it be that I forgot to add a bootstrap file or is it a TYPO3 problem?

Thanks a lot already

Answer 1

I found the problem. i overwrote a class in the CSS file.

#mainnavigation{
    display: flex;
    flex-direction: row-reverse;
    flex: none;
    flex-grow: 0;
    flex-shrink: 0;
    flex-basis: auto;
}