Change header column widths

I’ve created a child theme for the directory theme and want to change the width of the columns in the header to make the left column wider.

Currently the header has two columns. From looking at the source code of the page the columns look like the code below. I’ve removed the content between the div tags just to keep things clearer.

<div class=”col-md-6 col-sm-6 col-xs-12″ id=”core_logo”></div>
<div class=”col-md-6 col-sm-6 col-xs-12″ id=”core_header_searchbox”></div>

I figure I can change the class to look like this so the left column is wider

<div class=”col-md-8 col-sm-8 col-xs-12″ id=”core_logo”></div>
<div class=”col-md-4 col-sm-4 col-xs-12″ id=”core_header_searchbox”></div>

But from looking at header.php the header code seems to be added to page using hooks like this

<?php echo hook_topmenu(_design_topmenu()).hook_header(_design_header()).hook_menu(_design_menu(),1); ?>
<?php hook_container_before(); ?>

So the question is can I just replace the hooks with the header content I want or is there a way to change the column widths and keep the hooks in place?

Hoping someone can help.

Mark.