<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <meta name="viewport" content="width=device-width,initial-scale=1.0"> <title>后台登陆</title> <style type="text/css"> body{background:#000;} @media(min-767px) and (max-979px){body{background:red;}} </style> </head> <body> </body> </html>