php – Programme sections for blocks on admin edit

Hi not sure how to explain this but here it goes.

Basically I’m quite new to wordpress development and I am trying ot create a website for a client. What I am strggling with is creating predefinded sections on which to put various blocks, I have treied to group blocks that I need together. Here is an image that might help explain enter image description here

There are some sections that I would like to be full width black, and within this the client can add or edit blocks, and some section will be just standard white. Curretly in wordpress when I add blocks it all gets put under ‘content’ and when I out put it in PHP there I can’t seem to find a way to seperate anything

      <?php
  if ( have_posts() ) :

      get_template_part( 'loop' );

  else :

      get_template_part( 'content', 'none' );

  endif;
  ?>

So thats the loop for content. Which I cannont have some blocks in a black section and some in a white section. Can anyone point me in the direction of how to achieve what I require?

Thanks