Premkambaliya/2048-Game — reverse-engineered prompt

Build me a simple browser version of the 2048 game using plain HTML, CSS, and JavaScript. I want a clean 4 by 4 board where numbered tiles slide with the arrow keys, matching numbers merge, the score updates as you play, and a new tile appears after each valid move. Make it feel smooth and easy to play, with nice colors for the different tile values and a layout that works on both desktop and phone screens.

Please include a restart button, a clear game over message when there are no moves left, and a win message when the player reaches 2048. Keep the design simple but polished, like a small casual web game someone can open in a browser and start playing right away. If you need to check the usual 2048 rules, look them up and follow the standard behavior.