如何使媒体查询工作css3

Question

我有CSS文件，我想让@media工作。媒体应该做以下事情： - 在移动版中，它应该只有一列信息。 - 在平板电脑版本（500-1024）中，它应为两列 - 在1024-1240宽度，它应该是三列 - 在宽度超过1240的屏幕中，将有四列。

我也想添加页脚，但它一直在页面顶部。

CSS

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-css -->

@charset "utf-8"; 
/*--playTime adobe colour--*/ 

body {
    margin: 5px; 
    background-color: rgb(247, 168, 84); 
}

/*-----978GS--------*/ 

.col {
    margin-left: 25px; 
    margin-right: 17px; 
    margin-bottom: 20px; 
    margin-top: 3px; 

}
.col-4 {
    width: 305px; 
    float: left;    
}
.col-6 {
    width: 474px; 
}

.col-12 {
    width: 978px; 
}
/*---end 978GS---*/ 

.img-responsive {
    width: 100%; 
}
.btn {
    border: 1px solid white;
    padding: 6px 10px;
    border-radius: 5px;
}

.btn-buy{    
    background-color: rgb(87, 218, 247);
    border-color: none; 
    font-family: 'Fjalla One', sans-serif;
}
.product-box{
    background-color: rgb(145, 210, 84);
    padding: 5px;
    box-sizing: content-box;   
}
.product-box h3{
    color: peachpuff;
    font-family: 'Fjalla One', sans-serif;
    font-size: 1.5em;
    margin-bottom: 0.5em;
    text-align: center;    
}
.product-box p{
    color: peachpuff;
    font-family: 'Poppins', sans-serif;
    margin-top: 3px;    
}

#text-container-header{
    text-align: left bottom; 
}

.clearfix {
    clear: both;
}


/*--end main --*/

/*----*/

#mainPageBanner {
    height: 200px;
    background-color: ;
    background-size: 1050px;
    background-image: url(../Bilder/barcelona.jpg); 
    align-content: center; 
}

/*--end mainbanner--*/

/*---Start banner-*/

#mainPageHeader {
    height: 10em;
    background-color: rgb(242, 73, 7);
    text-align: left; 
    margin-bottom: 15px;     
}

#logo{
    color: peachpuff; 
    text-decoration: none; 
    font-size: 3em;
    font-family: 'Fjalla One', sans-serif;
    display: inline-block;
    margin-top: 0.1em;
    margin-left: 0.10em;
    text-align: ; 
}

#mainPageNav{
    width: 978px; 
    margin: auto; 
    background-color: none;
}

#mainPageNav::after{
    content: ""; 
    display: block; 
    clear: both: 
}

ul{
    margin: 0; 
    padding: 0; 
    list-style: none; 
}

li{
    float: left; 
    width: 80px; 
    position: relative; 
}

 a{
   background-color:
   color: rgb(255, 255, 0);
   font-family: 'Fjalla One', sans-serif;
   text-align: left;
   padding-bottom: 10px;
   padding-top: 10px;
}   

/*--banner end--*/


/*--- Start Footer--*/ 

.mainPageFooter{
    text-align: center; 
    text-decoration-line: underline; 
}

/*--- ends footer --*/ 

/*---Start media Queries---*/

@media screen (min-width: 500px) and (max-width: 2040) {

    .col-4{
        width: 100%; 
    }
}

HTML

 <header id="mainPageHeader" class="col">
  <a id="logo" href="#ng">Zen</a>

  <nav id="mainPageNav" class="col-12">
    <ul>
      <li><a href="#ng">Home</a></li>
      <li><a href="#ng">Destinations</a></li>
      <li><a href="#ng">Travel</a></li>
      <li><a href="#ng">My Account</a></li>
      <li><a href="#ng">Contact</a></li>
    </ul>
  </nav>
  <!--end navi menu-->
</header>

<div id="mainPageBanner" class="col col-12">
  <div id="text-container-header">

    <p>Banner text</p>
  </div>
</div>

<!--End banner-->

<div id="mainContent">

  <article class="col col-4 col-8 product-box col-7">
    <div id="product-content-box">
      <h3>Las Vegas</h3>
      <img class="img-responsive" src="Bilder/lasvegas.jpg" alt="Las vegas">
      <p>A quem concursionibus ubi excepteur te officia. Ab ita sempiternum. Quae ingeniis ita aute cillum, legam tempor hic proident. Minim admodum iis laborum. O aute appellat aut multos imitarentur arbitror lorem incurreret. Varias aut admodum de malis,
        de doctrina cohaerescant.</p>
      <input class="btn btn-order" type="button" value="Bestill">
    </div>
  </article>

  <article class="col col-4 col-8 product-box col-7">
    <div id="product-content-box">
      <h3>Kyoto</h3>
      <img class="img-responsive" src="Bilder/kyoto.jpg" alt="Kyoto">
      <p>Commodo anim varias appellat illum se pariatur quorum quid in varias ad illum a aut quem laborum, malis nescius fidelissimae. Multos mentitum ne sint aute, est eu tractavissent. Doctrina quo commodo ea in labore si tamen. Se vidisse arbitrantur,
        vidisse instituendarum ut deserunt, voluptate o quamquam ea et fugiat relinqueret. Ab ea velit consequat, tempor malis summis aut quid quo admodum ea vidisse se mandaremus nulla admodum officia. </p>
      <input class="btn btn-order" type="button" value="Bestill">
    </div>
  </article>

  <article class="col col-4 col-8 product-box col-7">
    <div id="product-content-box">
      <h3>Tenerife</h3>
      <img class="img-responsive" src="Bilder/tenerife.jpg" alt="Tenerife">
      <p>Ab legam ullamco commodo. Offendit culpa ipsum senserit labore et quid officia cernantur se magna probant ne arbitrantur quo irure singulis quo consequat. Proident lorem labore singulis ipsum, sed tamen concursionibus. O nescius ex aliquip aut duis
        cernantur se lorem legam, magna litteris e voluptatibus, ad mentitum comprehenderit. Pariatur relinqueret quo cupidatat. Et duis sed lorem.</p>
      <input class="btn btn-order" type="button" value="Bestill">
    </div>
  </article>

  <article class="col col-4 col-8 product-box col-7">
    <div id="product-content-box">
      <h3>Paris</h3>
      <img class="img-responsive" src="Bilder/louvre.jpg" alt="Paris">
      <p>Laboris est quis, illum cernantur do praetermissum, quo ipsum cupidatat domesticarum si quamquam quorum varias ut esse ne do elit consequat efflorescere, hic si amet voluptate quo culpa est fabulas, incurreret sed quid commodo. Ubi lorem consequat
        an</p>
      <input class="btn btn-order" type="button" value="Bestill">
    </div>
  </article>

  <div class="clearfix"></div>


  <article class="col col-4 col-8 product-box col-7">
    <div id="product-content-box">
      <h3>Barcelona</h3>
      <img class="img-responsive" src="Bilder/barcelona.jpg" alt="Barcelona">
      <p>Ubi incurreret voluptatibus. Aut multos nulla ita pariatur et appellat amet aliqua consequat summis a cernantur eram aut aliquip eruditionem, vidisse noster ullamco incurreret. Expetendis dolore esse an tamen, an irure sempiternum. Ab a amet probant
        ubi quibusdam qui laboris, e nam fidelissimae ne possumus eu irure. Iis a aute legam amet te labore mandaremus ne quem fugiat. Deserunt arbitrantur est vidisse iis senserit id esse ne id excepteur quo laboris, voluptate quae dolore sed esse. Aut
        nulla elit velit tempor.</p>
      <input class="btn btn-order" type="button" value="Bestill">
    </div>
  </article>

  <article class="col col-4 col-8 product-box col-7">
    <div id="product-content-box">
      <h3>London</h3>
      <img class="img-responsive" src="Bilder/london.jpg" alt="London">
      <p>Consequat quem consequat ex quibusdam ut fore, sed laboris ab laboris se a legam laborum. Legam arbitror ita officia, qui eu sunt possumus. Vidisse praesentibus id laboris, illum non mentitum ab e quorum malis fugiat tempor, ut eram legam sed proident.
        Esse exercitation possumus tamen fabulas. Ubi aliqua dolore illum singulis, eram an consequat ubi fore. Mandaremus multos cernantur cupidatat aut sed occaecat exercitation, quamquam familiaritatem an mentitum do doctrina do varias incididunt.</p>
      <input class="btn btn-order" type="button" value="Bestill">
    </div>
  </article>

  <article class="col col-4 col-8 product-box col-7">
    <div id="product-content-box">
      <h3>Tokyo</h3>
      <img class="img-responsive" src="Bilder/tokyo.jpg" alt="Tokyo">
      <p>Qui minim offendit. Quo velit proident adipisicing an culpa fabulas ex aliqua enim. Fugiat ne ita quid iudicem. Eram cernantur ad voluptate. Ingeniis non litteris. Velit offendit concursionibus, anim possumus offendit, irure sed te multos expetendis
        ea o malis quamquam transferrem. Quae a appellat si aute.</p>
      <input class="btn btn-order" type="button" value="Bestill">
    </div>
  </article>

  <article class="col col-4 col-8 product-box col-7">
    <div id="product-content-box">
      <h3>Oslo</h3>
      <img class="img-responsive" src="Bilder/oslo.jpg" alt="Tokyo">
      <p>Ullamco quid veniam ad quis. Legam proident se singulis a voluptate quem in commodo voluptatibus. Varias expetendis despicationes. Eram iis e illum aliquip nam nam magna cillum irure tempor aut duis mentitum se velit nulla, appellat elit varias
        probant velit. Ut noster duis o eiusmod. Fabulas fidelissimae iis commodo si mentitum cillum appellat iis probant concursionibus ita ullamco, nisi iudicem do dolor quem, arbitror eram possumus, ullamco summis pariatur, esse quibusdam relinqueret,
        labore exquisitaque occaecat esse quamquam.</p>
      <input class="btn btn-order" type="button" value="Bestill">
    </div>
  </article>

  <footer id="mainPageFooter">
    <p>----Zen----</p>
  </footer>

</div>
</div>
</div>

Answer 1

可能是您错过了媒体查询中的and：

e.g。     @media screen 和（min-width：500px）和（max-width：2040）{

Answer 2

请查看此Link媒体查询。

将页脚设置为底部

.mainPageFooter{
    text-align: center; 
    text-decoration-line: underline; 
    position: absolute;
    bottom : 0;
}

Answer 3

为最大宽度添加px并确保使用说

@media screen (min-width: 500px) and (max-width: 2040px) {

    body{
      display:none;    
    }
}