Replacing class ID with ID contents

Hi, i am new to PHP but i have some common knowledge to recognizing commands and such.

in my page i have code like this

<div class="page_column page_column_first" id="page_column_1" style="width: 499px;"><div class="page_block_container" id="page_block_759"><div class="disignBoxFirst">
    <div class="boxFirstHeader"><div class="dbTitle">Up and Coming</div></div>

    <div class="boxContent"><div class="dbContentHtml"><p>This is a placeholder for up and coming news to be edited at News Time.</p></div></div>

So whatever class it is linked to say “boxContent” which is the name of a section on a .css file on the server, i want it take the information under that header and place it on that same line and doing something like

preg_replace

class="boxContent with style=“border: 0px;
background-color: transparent;
margin:10px auto 5px;”

Can somebody write something like that for me please or help me with it? It’s basically taking the css rule and converting it to inline Thanks