Retrieving your browsing history through a CAPTCHA angielski

Browsers also let us style how visited links look, using the :visited pseudo-class. This is also pretty helpful, as the purple links don't match the style of every website.

You might already be thinking of various ways to exploit this, perhaps using background-images to send GET requests to a server, or maybe by using window.getComputedStyle to get the colour of a link.