Use the link attribute in the document's head:
<head>
<link rel="stylesheet" type="text/css" href="/?originalUrl=https%3A%2F%2Friptutorial.com%2F%26quot%3Bstylesheet.css%26quot%3B%26gt%3B%26lt%3B%2Fhead%26gt%3B%253C%2Fcode">
You can also use stylesheets provided from websites via a content delivery network, or CDN for short. (for example, Bootstrap):
<head>
<link rel="stylesheet" href="/?originalUrl=https%3A%2F%2Friptutorial.com%2F%26quot%3Bhttps%3A%2F%2Fmaxcdn.bootstrapcdn.com%2Fbootstrap%2F3.3.7%2Fcss%2Fbootstrap.min.css%26quot%3B%2520integrity%3D%26quot%3Bsha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va%2BPmSTsz%2FK68vbdEjh4u%26quot%3B%2520crossorigin%3D%26quot%3Banonymous%26quot%3B%26gt%3B%26lt%3B%2Fhead%26gt%3B%253C%2Fcode">
Generally, you can find CDN support for a framework on its website.