Reduce header width | WordPress.org

Your CSS should work unless something else is overriding it (perhaps due to improper placement).

But I don’t see it on your site currently.

Where did you add the custom CSS? If you’ve removed it, please add it back in APPEARANCE > CUSTOMIZE > ADDITIONAL CSS, and let me know so I can check to see what may be overriding it.

Standing by.

I’d removed the code as it wasn’t working but I’ve added it back now, thank you for having a look.

I can get the desired result by changing the width %, or adjusting the padding, but this then messes up the mobile view as it squashes the logo and menu too much.

All I see is (no selector):

max-width: 1200px; 
    margin: 0 auto;

This is not targeting the “site-header container” like you mentioned in your original post.

Change it to this:

.site-header {
    max-width: 1200px; 
    margin: 0 auto;
}

… and report back so I can take a look again (if it’s still not working).

That did the trick thank you so much!