st.css

* {
    box-sizing: border-box;
}
body {
    background: #87ceeb;
    height: 825px;
    width: 700px;
    border: 5px solid #48cd31;
    color: white;
    margin: 50px;
}
main {
    margin: 40px;
    text-align: left;
    font-size: 20px;
}
h1 {
    margin-top: 40px;
    text-align: center;
}
h2 {
    font-weight: bold;
}
nav {
    font-weight: bold;
}
nav a {
    display: inline-block;
    color: #4acc99;
}
nav ul li {
    display: inline;
    list-style-type: none;
    font-size: 20px;
}
ul {
    text-align: center;
}
li + li {
    border-left: 2px solid #818f95;
    padding: 0 5px 0 5px;
}
img {
    float: right;
    margin: 1em;
}