Unique widget id in sidebar

No offense, but your code is a COMPLETE mess, so I’m just going to give you clean code and then tell you how to target it.

register_sidebar( array(
        'name' => 'Post Sidebar',
        'before_widget' => '<div id="%1$s" class="widget widget-%2$s">',
        'after_widget'  => '</div>',
        'before_title'  => '<div class="titlediv">',
        'after_title'   => '</div>',
) );

Then to target the title via the id you can use CSS and say something like #id .titlediv. This way, you retain the ability to target the entire widget and you can target the title individually.

A word on the changes I made: I know you were wrapping the widget content in a <div>, but this is not the correct approach. Content wrapping like that should be done in the widget’s code, not at the widget definition code, as some widgets will not display correctly with that method.