从行类中删除z-index，并将z-index: 1;和position: relative;添加到页面容器类中。
这样，徽标和文本将位于行的上方。

body {
  padding: 0;
  margin: 0;
  background: #333;
}
.navbar{
  padding: 1rem;
  color: white;
  position: fixed;
  top: 0;
  height: 30px;
  width: 100%;
  z-index: 2;
  overflow: hidden;
}
.navbar.bg-dark {
  background-color: #333;
}

.navbar-logo {
  position:relative;
  font-style: italic;
  font-weight: bold;
  font-size: 24px;
  letter-spacing: 10px;
  z-index: 3;
}

.content {
  padding: 100px 20px;
  height: 600px;
  color: white;
  font-weight: bold;
}

.page-container {
  position: relative;
  max-width: 1024px;
  margin: 0 auto;
  z-index: 1;
}

/* Line */
.line {
  width: 100vw;
  left: 100px;
  height: 3px;
  background-color: #5c5c5c;
  position: absolute;
  transform-origin: left;  
  top: -1px;
}
.line.line-1 {
  transform: rotate(27.45deg);
}
.line.line-2 {
  transform: rotate(47deg);
}
.line.line-3 {
  transform: rotate(70deg);
}
.line.line-4 {
  transform: rotate(105deg);
}
.background {
  position: fixed;
}

<div class="navbar bg-dark">
  <div class="navbar-logo">
    Navbar Logo
  </div>
  <div class="line line-1"></div>
  <div class="line line-2"></div>
  <div class="line line-3"></div>
  <div class="line line-4"></div>
</div>

<div class="background line line-1"></div>
<div class="background line line-2"></div>
<div class="background line line-3"></div>
<div class="background line line-4"></div>

<div class="page-container">
  <div class="content">
  <p>It is a long established fact that a reader will be distracted by the readable content of a page when looking at its layout. The point of using Lorem Ipsum is that it has a more-or-less normal distribution of letters, as opposed to using 'Content here, content here', making it look like readable English. Many desktop publishing packages and web page editors now use Lorem Ipsum as their default model text, and a search for 'lorem ipsum' will uncover many web sites still in their infancy. Various versions have evolved over the years, sometimes by accident, sometimes on purpose (injected humour and the like).</p>
</div>
</div>

• • 编辑**：更改答案，使其看起来像屏幕截图，并使滚动正常工作。