html { 
    background: black; 
}

body { 
    background: white;
    color: black;
    padding: 30px; 
    width: 900px; 
    margin: 50px auto; 
    border: 2px solid green;
    border-radius: 15px; 
}

h1,
h3 { 
    color: black; 
    text-align: center; 

} 

h1 { 
    font-size:40pt; 
}




nav a{ 
    display: inline-block;
    color: black;
    text-decoration: none;
    border: 2px solid blue;
    padding: 10px;
    border-radius: 10px;
    margin-left: 170px; 
}

nav a:hover { 
    background-color: green;
    color:black; 
}

p { 
    text-align: center;
}

img, 
iframe { 
    display: block;
    margin: 10px auto;
    border: 2px solid white;
    border-radius: 10 px;
}

footer { 
    text-align: center; 
    color: green;
    margin-top: 50px;
}

ol, 
ul { 
    display: block;
    text-align: center;
    width: 150px;
    margin: 10px auto;
}