Mark introduction of section as part of a sentence

I want to mark the first words of a section as important and bold the text. Semantically, the first words work as an anchor of the beginning of a section (series of paragraphs), without the use of a separate heading.

An example of a website for inspiration: Een dubbel bestaan – De Groene Amsterdammer

Here is my site Read-Only: LINK
(how to share your site Read-Only link)