在您的例子中，body只有一个直接子节点，因此没有什么需要间隔的。
一般来说，在body上应用flexbox并不是一个好主意，因为你有一个整体的容器，所以在上面使用flexbox。

@import url('https://fonts.googleapis.com/css2?family=Roboto:wght@400;700&display=swap');
body {
  height: 100vh;
  margin: 0;
  overflow: hidden;
  font-family: Roboto, sans-serif;
}

.page-container {
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  height: 100%;
}

img {
  width: 600px;
}

button {
  font-family: Roboto, sans-serif;
  border: none;
  border-radius: 8px;
  background: #eee;
}

input {
  border: 1px solid #ddd;
  border-radius: 16px;
  padding: 8px 24px;
  width: 400px;
  margin-bottom: 16px;
}

li {
  list-style-type: none;
}

a {
  color: inherit;
  text-decoration: none;
}

.header {
  display: flex;
  justify-content: space-between;
}

.left-links,
.right-links {
  padding-left: 8px;
  padding-right: 8px;
  display: flex;
  gap: 5px;
}

.content {
  display: flex;
  flex-direction: column;
  align-items: center;
}

.footer {
  display: flex;
  justify-content: space-between;
  background-color: #eeeeee;
}

body {
  display: flex;
  flex-direction: column;
  height: 100vh;
  justify-content: space-between;
}

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