fixing footer at the bottom
<div class="page">
<div class="page__inner">
<header class="header">
<div class="header__inner">
</div>
</header>
<nav class="nav">
<div class="nav__inner">
</div>
</nav>
<main class="wrapper">
<div class="wrapper__inner">
<div class="content">
<div class="content__inner">
</div>
</div>
<div class="sidebar">
<div class="sidebar__inner">
</div>
</div>
</div>
</main>
<footer class="footer">
<div class="footer__inner">
</div>
</footer>
</div>
</div>