From example in the Vue 2 Cookbook docs, set up as inline style on the page itself.

body {
  display: flex;
  justify-content: center;
  background: #7E8D85;
  font-family: "Roboto Slab", serif;
  line-height: 1.4;
}

#app {
  margin-top: 20px;
  width: 300px;
  padding: 0 40px 40px;
  background: #2F242C;
  border-radius: 5px;
  color: #B3BFB8;
}

h1 {
  color: #F0F7F4;
}

.lighten {
  color: white;
}