JavaScript로 CSS 규칙을 동적으로 삽입하는 방법은 무엇입니까?

<code class="javascript">// Define your CSS as text
var styles = `
    .qwebirc-qui .ircwindow div { 
        font-family: Georgia,Cambria,"Times New Roman",Times,serif;
        margin: 26px auto 0 auto;
        max-width: 650px;
    }
    .qwebirc-qui .lines {
        font-size: 18px;
        line-height: 1.58;
        letter-spacing: -.004em;
    }
    
    .qwebirc-qui .nicklist a {
        margin: 6px;
    }
`

// Create a style node
var styleSheet = document.createElement("style")

// Assign the CSS text to the style node
styleSheet.textContent = styles

// Append the style node to the document head
document.head.appendChild(styleSheet)</code>