When using CSS, how do you set a specific directory's background color and such?

Sorry, I thought the thread title might have a limit

Now, let me give you some background information.

Earlier today, I started off searching for a good web provider that offered a cPanel because I am fairly new and do not understand FTP ports and whatnot. I found ByetHost. I made my website and made a few directories: about, contact, etc.

Anyways, I am working on the directory called 'main' right now.

Website: http://crossfirecheats.byethost10.com/Main/MainHTML.html

Anyways, I was trying to set the H1 header to white, and the background color to black. I thought this was a simple, global action I could do in a .CSS file and it would work on all elements; apparently not.

This is the CSS file's source:

body{background-color:black;} h1{color:white;}

This is the HTML file's source:

<html>
<title>CF Cheats</title>
<header>
    <link rel="Website Icon" href="/Up/Main/favicon.ico" />
    <h1>Hello, and welcome to Levi's CrossFire Tools</h1>
</header>
<body>
    <h3>+Main</h3>
    <h5>Here you will be able to view the available pages and get some background information.</h5>
    <a href="http://CrossFireCheats.byethost10.com/Main/MainHTML.html">|Go to main.</a>

    <h3>+Contact</h3>
    <h5>Want something added (suggestions)? Need support? Look no further :]</h5>
    <a href="http://CrossFireCheats.byethost10.com/Contact/ContactMainHTML.html">|Go to contact.</a>

    <h3>+Strategies</h3>
    <h5>Need some good strategies? You found 'em.</h5>
    <a href="http://CrossFireCheats.byethost10.com/Strategies/StrategiesMainHTML.html">|Go to strategies.</a>

    <h3>+Downloads</h3>
    <h5>Here you are able to download any files we provide!</h5>
    <a href="http://CrossFireCheats.byethost10.com/Downloads/DownloadsMainHTML.html">|Go to downloads.</a>

    <h3>+About</h3>
    <h5>Lea about why this website was created.</h5>
    <a href="http://CrossFireCheats.byethost10.com/About/AboutMainHTML.html">|Go to about.</a>

    <h4>Developed solely be Levi Branch. Site ruing since 02/15/2016 (MM/DD/YYYY)</h4>
    <h5>Website graciously provided by ByetHost.</h5>
</body>

The closing html tag isn't showing up btw? Strange, but anyways, it IS there.

Now, not sure if this is relevant or not, but here is the layout so far:

root About Main MainCSS.css MainHTML.html favicon.ico Downloads Contact Strategies

I don't know much about web development, and I am open to any suggestions. I would also like to know what I am doing wrong regarding this issue and web things in general as well as posting this here on StackOverflow, because this is my first post (Did I do anything wrong?).

If I forgot any information, please tell me!