Lange: Changing the text/background color of a single page using CSS

Any help is appreciated! I'm having a hard time figuring out how to change the background color (as well as text color) of a single page on my site. I'm currently using the Lange template. I've done a ton of research and have found various solutions but would really like to use CSS. I've taken the below code and implemented it into the index page under settings > advanced with no luck.

    <style>
   body#collection-5d18349a84a155000110af0c {
       background: #000000;
    }
   </style>

For reference, here's the link to the page I'd like black with white text - http://www.edwinsong.com/surface-gridiron-challenge

Thank you in advance!

@imedwin body#collection-5d18349a84a155000110af0c is Page ID. Each Page will have an ID. See how to check Page ID. https://beaverhero.com/squarespace-how-to/

So, your page ID is body#collection-5d18349a84a155000110af0c

So you need to use (wrap in style tag, or add to Home > Design > Custom CSS)

body#collection-5d18349a84a155000110af0c #site {
   background: #000000;
}

@tuanphan Thank you so much! The code you provided did work however I'm still seeing a narrow white bar in the header on the top of the page. I'm not sure what is causing this. Please help!

@imedwin you can use

header#header {
   margin-top: 0 !important;
}

@tuanphan Again, thank you! Worked like a charm. Is changing the text color to white as simple? Do I have to attribute text colors for each h1, h3 or title description segments or can I have one code that works globally on this page?

@imedwin h1, h3 {color: white;}if it doesn't work, try h1, h3 {color: white !important;}

@imedwin or change all to white :D

body#collection-5d18349a84a155000110af0c * {
   color: white;
}

@tuanphan Everything worked! Didn't see your code to change text globally but this is what I implemented and it seemed to work to change everything. Thank you for all your help!

p, h1, h3 {color: white !important; font-weight: 200;}