Need help with CSS

OK great!

So if I understand your question correctly you want to achieve this:

In which case, take your three divs: header_logo, header_center, header_right and move them inside the header div. So you now have:

<div id="header">
  <div id="header_logo">
      <h2>This is a logo in a div element</h2>
  </div>
    <div id="header_center">
      <h2>This is the center in a div element</h2>
  </div>
  <div id="header_right">
    <h2>This is the right border in a div element</h2>
  </div>
</div>

That puts your elements inside the header. However, they will naturally appear one below each other. To change that so they flow left to right across the page, you can change your CSS and make use of flexbox.

Add this extra line to your header div CSS:

#header {
    width: 960px;
    height: 80px;
    background-color: powderblue;
    display: flex;
}

This will achieve the screenshot I posted. Hopefully I didn't misunderstand and this is of some help - but let me know if not!

Thanks, someone have already answered your question :)