CodePen

HTML

            
              <div class="wrapper">

    <div class="block1">
    </div>

    <div class="block2">
    </div>
</div>


 
            
          
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↑ Insert the most common viewport meta tag

CSS

            
              body {
border: solid 1px green;
}
.wrapper {
border: solid 1px red;
display: table;
}
div { display: block; }
.block1 {
float: left;
width: 390px;
height: 390px;
background-color: blue;
}
.block2 {
float: left;
width: 390px;
height: 390px;
background-color: yellow;
}

@media (max-width: 783px) {
 .wrapper {
    max-width: 390px;
  }
}
            
          
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JS

            
              
            
          
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