<!DOCTYPE html> <html lang="zh-CN"> <head> <meta charset="utf-8"> <title>root</title> <style type="text/css"> @media (max-width : 479px) { html { font-size: 12px; } } @media (min-width : 480px) and (max-width : 779px) { html { font-size: 14px; } } @media (min-width : 780px) and (max-width : 979px) { html { font-size: 16px; } } @media (min-width : 980px) and (max-width : 1199px) { html { font-size: 18px; } } @media (min-width : 1200px) { html { font-size: 20px; } } </style> </head> <body> <h1 style="font-size: 1rem;padding: 1rem;">Hello World!</h1> </body> </html>