[Theme: Twenty Twelve] Lay-out crashes when resizing browser

Start with the mark-up errors:

https://validator.w3.org/check?uri=http%3A%2F%2Fwww.nielstammes.nl%2Ftestomgeving%2F&charset=%28detect+automatically%29&doctype=Inline&group=0

And you should be using a Child Theme for any modifications-

https://codex.www.ads-software.com/Child_Themes

I think this happens because of the mobile lay-out that is build in the theme.

no – more likely caused by whatever edits you have made to style.css

when working with one of the default themes, strongly consider to create a child theme to make the customisations with, or for pure formatting adaptions, use a custom css plugin (like the custom css of ‘jetpack’).
https://www.ads-software.com/extend/plugins/jetpack/
https://codex.www.ads-software.com/Child_Themes

Thanks for you answer. I will fix the errors, but i don’t think that is the problem. If you look at the preview of the theme: https://wp-themes.com/twentytwelve/ you can see that it does the same as my website. Is there a way to “remove” the code that changes my website (and the preview website of the theme) when i change to a smaller browser.

@alchymyth
I will look at that.

That is intentional. Twenty Twelve is a mobile theme.

I advise you not to use a mobile theme.

related: https://www.ads-software.com/support/topic/remove-the-responsive-code-from-the-twenty-tewlve-theme?replies=21

Thanks a lot!
I did manage to disable the responsive design. One more question: If i now change the width of my browser to a smaller resolution all the text of the website comes togheter (Home page text, navigation text and header text. How can i fix the width of my website, so that if i watch on a smaller browser, i see just a part of the website (a part of the whole website i would see if i would watch on a bigger screen).

Thanks in advance.