TwentyEleven: Single post view align with header

Hi,

I am setting up a new website and Having trouble with one setting.

In my post feed the text is aligned with the header (I changed that in the style.css)
(https://rave-cruitment.com/wp)

but in single post view the text is indent to the right. I want this also to align with the header but cannot find the place to change this.
(https://rave-cruitment.com/wp/2021)

Any help is much appreciated