Try it Live

<!DOCTYPE html>
<html>
 <head>
  <style>
   .flexbox-MQ {
    margin:10px;
    display: flex;
   }
   
   .child-val {
    padding: 5px;
    margin: 5px;
    width:60px;
    height:60px;
    text-align: center;
    border:1px solid black;
    background-color: #94C548;
   }
   
   @media (max-width: 500px), (min-width: 700px) {
    .flexbox-MQ {display: grid;}
   }
  </style>
 </head>
 <body>
   <p style="font-size:2em;">CSS Complex media queries <b>(comma) ","</b></p>
      The media query will be true if
      <ol>
	    <li>flexbox maximum width is 500px(i.e. less than or equal to 500px)
	     OR
	  	<li>flexbox minimum width is 700px(i.e. width more than or equal to 700px)
	  </ol>
      so, if any 1 of these media query is true the
	  entire media expression is true. 	  
   <div class="flexbox-MQ">
     <div class="child-val" style="flex-grow: 1">BOX 1</div>
     <div class="child-val" style="flex-grow: 1">BOX 2</div>
     <div class="child-val" style="flex-grow: 1">BOX 3</div>
     <div class="child-val" style="flex-grow: 1">BOX 4</div>
   </div>
 </body>
</html>

​x
 
<!DOCTYPE html>
<html>
 <head>
  <style>
   .flexbox-MQ {
    margin:10px;
    display: flex;
   }
   
   .child-val {
    padding: 5px;
    margin: 5px;
    width:60px;
    height:60px;
    text-align: center;
    border:1px solid black;
    background-color: #94C548;
   }
   
   @media (max-width: 500px), (min-width: 700px) {
    .flexbox-MQ {display: grid;}
   }
  </style>
 </head>
 <body>
   <p style="font-size:2em;">CSS Complex media queries <b>(comma) ","</b></p>
      The media query will be true if
      <ol>
        <li>flexbox maximum width is 500px(i.e. less than or equal to 500px)
         OR
        <li>flexbox minimum width is 700px(i.e. width more than or equal to 700px)
      </ol>
      so, if any 1 of these media query is true the
      entire media expression is true.    
   <div class="flexbox-MQ">
     <div class="child-val" style="flex-grow: 1">BOX 1</div>
     <div class="child-val" style="flex-grow: 1">BOX 2</div>
     <div class="child-val" style="flex-grow: 1">BOX 3</div>
     <div class="child-val" style="flex-grow: 1">BOX 4</div>
   </div>
 </body>
</html>
​