Untitled

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
    *
    {
        margin:0;
        padding:0;
    }
     header
     {
         text-align: center;
       width: 100%;
       height: 40px;
       background-color: #000;
         color:#fff;
     }
     footer
     {
        text-align: center;
         width: 100%;
         height: 40px;

         /* position:absolute;
         bottom:0; */
         background-color: #000;
         color:#fff;
     }
     .a
     {
        border:1px solid black;
        border:black;
        text-align: center;
        background-color: gray;
        color: gray;
        width: 100px;
        height: 500px;
        display: inline-block;
        vertical-align: middle;
     }
     .b
     {
        border:1px solid black;
        width: 100px;
        height: 500px;
        text-align: center;
        display: inline-block;
        vertical-align: middle;
     }
     .c
     {
        border:1px solid black;
        width: calc(100% - 423px);
        height: 500px;
        text-align: center;
        display: inline-block;
        vertical-align: middle;
     }
    </style>
</head>
<body>
    <header>Header</header>
    <div class="a">a</div>
    <div class="b">F<br>I<br>X<br>E<br>D</div>
    <div class="c">Fluid</div>
    <div class="b">F<br>I<br>X<br>E<br>D</div>
    <div class="a">a</div>
    <footer>Footer</footer>
</body>
</html>