Content in flexbox with minimum size

Question

I am using a flexbox to vertically align a div, with variable height, in its container (I'm open to other options). But I struggle to get a reliable scroll behavior when the container is smaller than the content.

html,
body,
.app {
  height: 100%;
}

.app {
  background-color: blue;
  color: white;
}

.app header {
  height: 80px;
  background-color: red;
}

.app .container {
  display: flex;
  flex-direction: column;
  background-color: black;
  height: calc(100% - 80px);
  align-items: center;
  justify-content: center;
  overflow: scroll;
}

.app .container .content {
  width: 300px;
  height: 200px;
  background-color: yellow;
  color: black;
}

<link rel="stylesheet prefetch" href="https://cdnjs.cloudflare.com/ajax/libs/meyer-reset/2.0/reset.min.css">
<div class="app">
  <header>Header</header>
  <div class="container">
    <div class="content">
      Variable content height
    </div>
  </div>
</div>

Thanks a lot!

Answer 1

Keep overflow:auto and no need to use column as direction, simply keep it row. Then rely on margin:auto to keep the element centred:

Example with no overflow and centred:

html, body, .app {
  height: 100%;
}
body {
 margin:0;
}

.app {
  background-color: blue;
  color: white;
}
.app header {
  height: 80px;
  background-color: red;
}
.app .container {
  display: flex;
  flex-direction: row;
  background-color: black;
  height: calc(100% - 80px);
  justify-content: center;
  overflow: auto;
}
.app .container .content {
  width: 300px;
  height:100px;
  background-color: yellow;
  color: black;
  margin:auto;
}

<div class="app">
  <header>Header</header>
  <div class="container">
    <div class="content">
      Variable content height
    </div>
  </div>
</div>

Example with overflow and scroll

html, body, .app {
  height: 100%;
}
body {
 margin:0;
}

.app {
  background-color: blue;
  color: white;
}
.app header {
  height: 80px;
  background-color: red;
}
.app .container {
  display: flex;
  flex-direction: row;
  background-color: black;
  height: calc(100% - 80px);
  justify-content: center;
  overflow: auto;
}
.app .container .content {
  width: 300px;
  height:900px;
  background-color: yellow;
  color: black;
  margin:auto;
}

<div class="app">
  <header>Header</header>
  <div class="container">
    <div class="content">
      Variable content height
    </div>
  </div>
</div>