媒体查询的代码：
<!DOCTYPE html><html> <head> <meta charset="UTF-8"> <title></title> <style> .a {
border: 1px solid #000000;
width: 100px;
height: 100px;
background-color: #000000;
}
@media only screen and (min-width: 300px) and (max-width: 0px) {
.a {
background-color: red;
}
} @media only screen and (min-width: 700px) {
.a {
background-color: green;
}
} @media only screen and (max-width:200px ) {
.a {
background-color: blue;
}
} </style> </head> <body> <p class="a"></p> </body></html>