html, 
body {
    height: 100%;
}

body {
  font: 14px/1.5 Helvetica Neue,Helvetica,Arial,Microsoft Yahei,Hiragino Sans GB,Heiti SC,WenQuanYi Micro Hei,sans-serif;
  color: #333;
  background-color: #fff;
  margin: 0;
}
#backgroundImage {
  border: none;
  height: 100%;
  pointer-events: none;
  position: fixed;
  top: 0;
  width: 100%;
  visibility: visible;
}

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

#content {
  z-index: 1;

}

#box {
  width: 400px;
  height: 225px;
}

header {
  font-family: cursive;
  font-size: 2.5rem;
  border-bottom: solid 1px #33333394;
  text-shadow: 3px 2px 6px #333;
}

main {
  flex-grow: 2;
}

p {
  align-self: flex-start;
  font-size: 1.2rem;
  text-shadow: 0 1px 1px #333;
}

a {
  text-decoration: none;
}