It exceeds the post text because it’s longer than the space taken up by the post text, and it’s floated left, so any uncleared content will appear to the image’s right. The borders go behind the image because floats float over uncleared elements. They don’t change their width. And an element’s borders are not a part of its content.
I think this will fix it:
h2.post_title {
clear: left;
}
To implement this, please note that the only recommended way of modifying a theme is via a Child Theme. Child themes are trivially easy to create and protect you from having your changes overwritten by theme updates.
Once you have a child theme, you simply add the new style rule above to the end of the child theme’s style.css file, after the @import statement.
Of course, you can alter your theme directly. WordPress doesn’t force you to use a child theme. It’s up to you.
HTH
PAE
