侧边栏的内容会覆盖正文内容

Question

你能帮我吗？发生的情况是，内容侧边栏会覆盖内容的主体。谁能告诉我怎么了？

我正在使用物化框架。

   function loadNav() {
      var xhttp = new XMLHttpRequest();
      xhttp.onreadystatechange = function() {
        if (this.readyState == 4) {
          if (this.status != 200) return;

          // Muat daftar tautan menu
          document.querySelectorAll(".sidebar, .sidenav").forEach(function(elm) {
            elm.innerHTML = xhttp.responseText; 
          });

          // daftar event listener stiap menu
          document.querySelectorAll(".sidebar a, .sidenav a").forEach(function(elm) {
            elm.addEventListener("click",function(event) {    
              // close sidenav        
              var sidnav = document.querySelector(".sidenav");
              M.Sidenav.getInstance(sidnav).close();
              // content page
              page = event.target.getAttribute("href").substr(1);
              loadPage(page);
            });
          });
        }
      };
      xhttp.open("GET", "nav.html", true);
      xhttp.send();
    }

 <header>
    <nav class="top-nav grey darken-1" role="navigation">
      <div class="nav-wrapper container">          
        <a href="#" class="brand-logo">Submission PWA</a>
        <a href="#" class="sidenav-trigger" data-target="slide-out">☰</a>

        <ul class="sidebar hide-on-mobile-and-down"></ul>
        <ul class="sidenav sidenav-fixed" id="slide-out"></ul>     
      </div>      
    </nav>
  </header>