<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <title>rem自适应</title> <script> var c = () => { let w = document.documentElement.clientWidth; let n = (20 * (w / 320) > 40 ? 40 + "px" : 20 * (w / 320) > 40 + "px"); document.documentElement.style.fontSize = n; } window.addEventListener("load", c) window.addEventListener("resize", c) </script> <style> div { font-size: 1rem; } </style> </head> <body> <div>123</div> </body> </html>