html, body {
  width: 100%;
  height: 100%;
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
body {
/*background: url(https://subtlepatterns.com/patterns/white_texture.png);*/
  font: 100 14px sans-serif;
  color: #444555;
}

h1 {
  font-weight: 100;
  font-size: 2.7em;
  text-align: center;
  margin: 20px;
}

h3 {
  font-weight: 100;
  font-size: 1.8em;
  text-align: center;
  margin: 20px;
}

a {
  text-decoration: none;
  color: white;
  padding-right: 50px;
}

.wrapper {
  max-width: 900px;
  height: 100%;
  margin: 0px auto;
  padding: 10px;
  background-color: #fff;
  position: relative;
}

.center {
  width: 671px;
  background: #333;
  border-radius: 5px;
  color: white;
  padding: 20px;
}

.wrapper.flex {
  display: flex;
  justify-content: center;
  align-items: center;
}

.wrapper .center {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

.wrapper.flex .center {
  background: #333;
  border-radius: 5px;
  color: white;
  padding: 20px;
}