我的媒体查询不起作用。包括元标记； link 相对 link

Question

这里是编码初学者。我正在尝试为我的移动设备网站设置断点，以便我的网站适合小屏幕。我只是想检查如果我缩小视口的宽度，背景颜色是否会改变，但没有发生任何变化。也许我只是对一个简单的错误视而不见？

body {
 margin: 0;
 background-color: #4f4d4d;
 overflow-x:hidden;
 width: 100%;
 height: auto;
}

ul {
 margin-top: -80px;
 list-style-type: none;
}

li {
 font-size: 25px;
    float: right;
    font-weight: bold;
}

li a {
 display: block;
 text-decoration: none;
 text-align: center;
 font-family: sans-serif;
 color: white;
 border-left: 1px solid white;
 padding: 23px;
}

li a:visited {
 text-decoration: none;
 color: white;
 font-family: sans-serif;
}

li a:hover:not(.active) {
 background-color: #333;
}


#header {
 position: relative;
 width: 100%;
 height: 875px;
 background-image: url(../images/bg.jpg);
 background-repeat: no-repeat;
 background-size: 100% 100%;
}

#nav {
 width: 100%;
 height: 75px;
 background-color: black;
}

#logo {
 width: 75px;
 height: 75px;
}

#logo_text {
 position: absolute;
 display: inline;
 top: -10px;
 left: 80px;
 font-size: 30px;
 font-family: sans-serif;
 color: white;
 font-weight: bold;
}

#welcome_text_div {
 position: absolute;
 width: 1000px;
 height: 300px;
 top: 25%;
 left: 0;
 right: 0;
 margin: auto;
}

#welcome_text {
 color: white;
 font-family: sans-serif;
 text-transform: uppercase;
 font-weight: bold;
 font-size: 90px;
 text-align: center;
}

#welcome_under_text {
 color: white;
 font-family: sans-serif;
 text-align: center;
 font-weight: bold;
 margin-top: -80px;
 font-size: 25px;
}

#alumni_div {
 position: relative;
 height: 800px;
 width: 95%;
 margin-right: auto;
 margin-left: auto;
 top: 100px;
 margin-bottom: 50px;
}


.alumni_link:link {
 text-decoration: none;
}

.alumni_link:visited {
 color: white;
}

.alumni_link:hover {
 color: grey;
}

#alumni_1 {
 position: absolute;
 width: 25%;
 height: 100%;
 background-color: black;
 right: 77%;
}

#alumni_2 {
 position: absolute;
 width: 25%;
 height: 100%;
 background-color: blue;
 right: 51%;
}

#alumni_3 {
 position: absolute;
 width: 25%;
 height: 100%;
 background-color: red;
 left: 50.5%;
}

#alumni_4 {
 position: absolute;
 width: 25%;
 height: 100%;
 background-color: orange;
 left: 77%;
}

.alumni_text {
 font-family: sans-serif;
 font-weight: bold;
 font-size: 35px;
 margin-top: 300px;
 color: white;
 text-align: center;
}

.graduate_text {
 font-family: sans-serif;
 font-weight: bold;
 font-size: 20px;
 color: white;
 text-align: center;
}

<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="UTF-8">
 <meta name="viewport" content="width=device-width, initial-scale=1.0">
 <title>CLC Website</title>
 <link rel="stylesheet" href="main1.css">
 <link rel="stylesheet" media="mediatype and|not|only (media feature)" href="mystylesheet2.css">
</head>
<body>
 <div id="header">
  <div id="nav">
   <img src="../images/logo.png" id="logo" alt="logo">
   <p id="logo_text">CLC</p>
   <ul>
    <li><a href="#">Contact Us</a></li>
    <li><a href="#">Professors</a></li>
    <li><a href="#">Courses</a></li>
    <li><a href="#">About</a></li>
    <li><a href="#">Home</a></li>
   </ul>
  </div><!--/nav-->

  <div id="welcome_text_div">
   <p id="welcome_text">The Best Offer</p>
   <p id="welcome_under_text">Truth evades a single definition and true understanding requires a comparative perspective</p>
  </div><!--/welcome_text_div-->
 </div><!--/header-->

  <div id="alumni_div">
   <div id="alumni_1">
    <a href="#" class="alumni_link"><p class="alumni_text">Alumni Name <br> Class of 15</p><p class="graduate_text">Graduate School</p></a>
   </div>

   <div id="alumni_2">
    <a href="#" class="alumni_link"><p class="alumni_text">Alumni Name <br> Class of 14</p><p class="graduate_text">Company A</p></a>
   </div>

   <div id="alumni_3">
    <a href="#" class="alumni_link"><p class="alumni_text">Alumni Name <br> Class of 13</p><p class="graduate_text">Company B</p></a>
   </div>

   <div id="alumni_4">
    <a href="#" class="alumni_link"><p class="alumni_text">Alumni Name <br> Class of 12</p><p class="graduate_text">Company C</p></a>
   </div>
  </div><!--/alumni_div-->
</body>
</html>

@media only screen and (max-width: 1024px) {
 body {
 margin: 0;
 background-color: white;
 overflow-x:hidden;
 width: 100%;
 height: auto;
    }
}


@media only screen and (max-width: 767px) {
 body {
 margin: 0;
 background-color: red;
 overflow-x:hidden;
 width: 100%;
 height: auto;
    }
}

@media only screen and (max-width: 480px) {
 body {
 margin: 0;
 background-color: blue;
 overflow-x:hidden;
 width: 100%;
 height: auto;
    }  
}

Answer 1

See this fiddle

缺少括号，更像是这样：

@media only screen and (max-width: 1024px) {
    body {
      margin: 0;
      background-color: white;
      overflow-x:hidden;
      width: 100%;
      height: auto;
    }
}


@media only screen and (max-width: 767px) {
    body {
      margin: 0;
      background-color: red;
      overflow-x:hidden;
      width: 100%;
      height: auto;
    }
}

@media only screen and (max-width: 480px) {
    body {
      margin: 0;
      background-color: blue;
      overflow-x:hidden;
      width: 100%;
      height: auto;
    }
}

Answer 2

它在这里按预期工作。您是否将媒体查询置于所有其他 CSS 规则之下？如果没有，它们可以被后续规则覆盖。

ADDITION/EDIT（从注释上移）：在 HTML 中，从对第二个样式表的引用中取出 media="mediatype and|not|only (media feature)"。

我的媒体查询不起作用。包括元标记； link 相对 link

My Media Query does not work. Included Meta tag; link rel link

html

css

media-queries