居中一个具有100vh高度的背景图上的div-PHP中文网问答

我正在学习一门课程，其中顶部有一个固定位置的导航栏。背景设置为100vh的高度，带有文本内容的div位于背景的中心。使用 Flexbox 它几乎居中，但为了真正使其到达背景中心，该 div 的高度必须设置为 100% 的高度。我对 Flexbox 和视口高度有所了解，但是我对为什么需要将 div 的高度设置为 100% 才能真正使潜水居中感到困惑。我想你可以在这里放置任何图像作为背景来复制我所要求的内容。希望我在这里说得通。

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
  background: #fff;
  color: #333;
  line-height: 1.5;
}

ul {
  list-style: none;
}

a {
  color: #333;
  text-decoration: none;
}

h1,
h2 {
  font-weight: 300px;
  line-height: 1.5:
}

p {
  margin: 10px 0;
}

img {
  width: 100%;
  /*makes image width of the container */
}


/* navbar */

.navbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  background-color: #333;
  color: #fff;
  width: 100%;
  height: 70px;
  /* apparently a common height for navbar */
  position: fixed;
  top: 0px;
  padding: 0 30px;
}

.navbar a {
  color: #fff;
  padding: 10px 20px;
  margin: 0 5px;
}

.navbar a:hover {
  border-bottom: 1px solid #28a745;
}

.navbar ul {
  display: flex;
}


/* Header */

.hero {
  background: url("/img/home/showcase.jpg") no-repeat center center/cover;
  height: 100vh;
  position: relative;
  color: #fff;
}

.hero .content {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  height: 100%;
}

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Welcome to EdgeLedger</title>
  <link rel="stylesheet" href="/css/utilities.css">
  <!-- style.css is last in case utilities.css needs to be overwritten -->
  <link rel="stylesheet" href="/css/style.css">
  <script src="https://kit.fontawesome.com/6eab1538de.js" crossorigin="anonymous"></script>
</head>

<body id="home">
  <header class="hero">
    <div id="navbar" class="navbar">
      <h1 class="logo">
        <span class="text-primary"><i class="fas fa-book-open"></i>Edge</span>Ledger
      </h1>
      <nav>
        <ul>
          <li><a href="#home">Home</a></li>
          <li><a href="#about">About</a></li>
          <li><a href="#cases">Cases</a></li>
          <li><a href="#blog">Blog</a></li>
          <li><a href="#contact">Contact</a></li>
        </ul>
      </nav>
    </div>

    <div class="content">
      <h1>The sky is the limit</h1>
      <p>We provide world class financial assistance</p>
      <a href="#about" class="btn">Read More</a>
    </div>
  </header>
</body>

</html>