Thank you for your quick response and pointing me to understanding what was going on (sorry for not replying sooner)!
I added the following to my CSS, and now it displays without any margin:
html, body {
margin: 0;
}
I looked through my code and did not find any place where I had added a margin, so was curious where it might have been picking up the 8px value from? For future reference, is the margin property something I should be setting always if I want it full width?
The 8px is the default margin added by the browser default styles. You will see this on other elements like margin on headers or margin and padding on list elements etc.
Other than knowing about the default styles one tool you should learn is the Inspector (Chrome or Firefox) it is super helpful in better understanding your layout and the box model. I suggest learning the browser developer tools (Video) as much as possible.