Centering an entire post on a page

I have a blog here ..... http://www.beyondbridges.net - i am using tonal as my template - I have installed a child theme - I am a css beginner - but definitely moving along at a pace ... the plug in 'child theme configurator' has proven awesome in my learning. i know how to inspect elements and adjust settings .... GENERALLY - i seem to have even cracked @media queries ... so here is my problem - that i KNOW is going to be a doddle for you savvy people.

how do i ensure that the entire post and post stream is centered under the main image - i know i have but padding left in various places and the posts and home page - barring a few nuances I am still working through looks like I want it t - But I just now want to center it all under the header image - ideally the post titles should span the full width of the picture - but if not - at least centered and likewise the block content underneath

can anyone help?

my thanks in eager anticipation