SkittlesGod-cmd/Login-Templates ? reverse-engineered prompt

Build me a small set of polished login page templates I can drop into a website without much setup. I want them to feel modern, clean, and professional, and they should work well on both desktop and mobile.

Please include a few different looks so I can choose what fits my site best, like a simple login and signup version, a greyscale style, and a warmer coffee inspired style. Each page should have nice form styling, basic JavaScript validation, and a smooth user experience in major browsers. Keep everything easy to customize so I can quickly swap colors, text, fonts, and branding later.

Use plain HTML, CSS, and JavaScript, and make the files simple enough that I can copy them into another project. If it makes sense, add small interactive touches that improve the feel without making it complicated. Look up current best practices online if you need to, but keep the final result lightweight and straightforward.