solved with flexbox - fixed sidebars with fluid center

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<body class="app">
    <header class="app__navbar"></header>
    <main class="app__body">
        <div class="app__main">
          
          <div class="center-area"><p>Center Area</p></div>
          <div class="left-sidebar"><p>Left Sidebar</p></div>
          <div class="right-sidebar"><p>Right Sidebar</p></div>
      
        </div>
        <footer></footer>
    </main>
</body>
    