Submit post: Disable all HTML tags

Hi,

how to make the posted content by the user saved without HTML tags?

I added this in my function.php themes child:
add_filter( 'save_post', 'wp_filter_nohtml_kses');
also:
add_action( 'save_post', 'wp_filter_nohtml_kses');

But it’s not work. ?? My user still can submit post by html tags they created and it’s really annoying. They make the font bigger, smaller, then bigest, small again..and so on.. by HTML:
<div style="font-size:50px">blabla</div><div style="font-size:8px">blabla</div> and so on..

Any ways to prevent this?
Thank you.

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