* {
  margin: 0;
  padding:0;
}

html, body {
  height: 100%;
}

body {
  font-family: Arial, Helvetica, sans-serif;
}

div {
  box-sizing: border-box;
}

p {
  margin: 1em 0;
}


.flex-container {
  display: flex;
  min-height: 100%;
  background-color: #333;
  color: yellow;
  align-items: center;
}

.flex-content {
flex: 1;
}

.inner {
  margin: 0 auto;
  padding: 1em;
  font-size: 2em;
  border: 1px solid yellow;
  max-width: 10em;
}