.title{
    text-align: center;
}

#subtitle {
    text-align: center;
    font-size: large;
}

.container {
    margin: auto;
    color: blue;
    border-radius: 10px;
    padding: 15px;
    width: 400px;
    height: 640px;
    background-color: aliceblue;
}

/* 选择器的优先级 */
.container::before {
    content: "Hi";
    color: green; 
}

.container::after {
    content: "Bye";
    color:green;
} 

 a[href="https://www.sciencefocus.com/science/fun-facts"]:hover {
    color:red;
} 

.container::first-line {
    color: red;
}