Hi there,
It is actually quite hard to change the DOM just using CSS and it is also harder to keep track of the customization in the future.
By the way, all themes in EasyBlog inherited theme files from Wireframe. So, in your case, it is actually this file is rendering your <h1> tag.
/components/com_easyblog/themes/wireframe/blogs/entry/default.posts.php
You can utilize our theme overrides feature at the EasyBlog. Navigate to EasyBlog > Themes > (wireframe) > (search desired file) > (add modification) > Save. Please checkout my screenshot:
http://take.ms/BnYj9 .
Hope this helps.