underscores.me template-part seems to be absolutely positioned

I’m not sure how to describe what’s going on. I’m using the underscores.me starter template to develop a custom theme. I’m working on the “page.php” template, and I’ve run into a slight roadblock. when I call my header, then use the loop to generate my content the loop lays under the header. Not entirely, as the text appears under the header, but there is still whitespace behind the header, so if I were to try and add a top margin to the content area it would not be visible unless i used a high number, like margin-top: 400px or something. underscores.me uses template parts to call the different sections, so on my page.php template, i call my header, then I call the template part for content-page. within the content-page is where i can edit how the loop looks. the problem is that content-page seems to be setting itself to 100% and absolute positioning itself to the top. I’ve inspected everywhere I can think to look in all parts of the template and can’t find what is causing this. I’ve also been using firebug to try and find it, but still, no luck.

I’ve only got a local version of the site, so I can’t share a link, but here are some images that hopefully you can get a better idea of what I’m trying to describe here.

This is an image of how it looks as it is

this is an image of how it looks when I declare “.entry-content” to be positioned relatively. this is to help describe the whitespace i’m talking about that gets created “under” the header

Any help or advice would be great! If there is any more info I can provide to help clarify my question, please let me know.
Thanks!