Hello Marta,
Thank you for your question about modifying the “wedge” transition. This can certainly be modified without switching the theme. You can use the following CSS modification:
.entry-content .bgtfw > .container-fluid { position: inherit; }
This is only one of thousands of ways to modify the theme. I caution that this kind of modification can affect other themes you might be working with in the staging area. As long as you are aware of that, you can make considerations wisely, and you could likewise disable the modification if you were thinking about switching to another theme.
To use this CSS snippet, you will go into the Customizer, click on the Advanced tab, and open the CSS & JS editors.
Best,
Christopher M.