Hi @rcinus,
I hope you are well today and thank you for your questions.
1) change the heart icon on the blog but I can’t find the image in the team or css rule in section-divider
The heart icon is created using font awesome and not image.
You can try changing it by using the solution posted in the following topics.
https://colorlibsupport.com/t/unite-blog-customization/
https://colorlibsupport.com/t/section-divider-hr-section-divider-css-modification-has-no-effect/#post-59590
2) show more than 3 blog posts on the blog page but despite I selected 7 in general reading site options I still got just 3.
Could you please share me the blog page URL from your site and the screenshot of general reading settings where it is not displaying correctly so that i can troubleshoot it?
3) in the mobile version of the page widget are not responsive when resizing, see screenshot attached could you please help me to fix this?
To help us keep support thread separates could you please create new thread for your other questions here Unite Theme - Colorlib Support Forum instead of asking them in your single thread as it makes the thread messy and hard to read.
If you want to you can also add reference of this thread in your newly created thread.
We would be more than happy to help you on your new thread.
Best Regards,
Movin