How to add styles directly in Rich Text Editor in Umbraco 10

I'm trying to write styles directly in the content of Rich text Editor in Umbraco 10, but that was not working and after writing style and saving it, the whole RTE getting white and when opening the source code all content and styles are disappearing. I've searched the forums and haven't found a solution that could fix the issue for me.
Can anyone help me?

Please help me how to add styles directly in content of RTE in umbraco 10

Have you (googled and) taken a look at https://docs.umbraco.com/umbraco-cms/v/10.latest-lts/reference/configuration/richtexteditorsettings already?

Not entirely sure I'm following what you are trying to do, but if you configure "validElements" to include "style" (like in the example in the link) you should be allowed to have a <style> tag in your RTE code.

If you are trying to inline styles via a style attribute on some other element, you can configure that too.

Say you want to add style="something: something" to a div, should be able to add +div[style] to the validElements config.

And of course, if there is no RichTextEditor section in your appsettings.json, you'll need to add it yourself, just like in the example on Umbraco Docs.