This example demonstrates the use of vanilla JavaScript and CSS to handle basic user input and display dynamic text on a web page. It shows a prompt-based grade calculator that assigns letter grades (A through F) based on a numeric score, along with corresponding feedback messages, and also displays the current day of the week using a switch statement on `new Date().getDay()`. The page uses `document.write()` for output and a simple `style.css` file with a custom `g2` element style, though no React or specific data-visualization libraries are involved.