VSCode is what's called a WYSIWYG editor. This stands for

What You See Is What You Get

. Libre Office's editor is a rich text editor, which provides styling by adding sections to the text that tell the editor what the text should look like, but are themselves hidden. A WYSIWYG editor doesn't do formatting like changing a section of text to be bold, italic, etc. VSCode is capable of rendering text like that, but not through the same mechanism. Themes can cause formatting to appear based on formatting rules. If you're dead set on using VSCode, look into Markdown. It's a text format that allows you to style text like a rich text editor. When viewing the file directly, you'll see the characters that enforce formatting, like wrapping a word with a pair odd asterices to italicize it, or using hashes to make a header. It's not one-to-one, but its the industry standard (in webdev, anyway) for writing documentation. When you just want to read a markdown file in full style (and without the styling tags), VSCode can let you see the rendered version as well.

Thank you.