html {
  height: 100%;
  overflow: hidden;
}
body {
  background: url("https://images.pexels.com/photos/1252869/pexels-photo-1252869.jpeg?auto=compress&cs=tinysrgb&dpr=2&h=650&w=940") no-repeat center center fixed;
  color: #fff;
  font-family: sans-serif;
  text-align: center;
  min-height: 100%;
  display: flex;
  justify-content: center;
  align-items: center;
}
h1 {
  font-size: 2.5rem;
  text-shadow: 1px 1px 5px #000;  
  margin: 0;
}
p {
  font-size: 1.2rem;  
  text-shadow: 1px 1px 2px #000;
}
a {
  color: #fff;
}
#countdown {
  max-width: 450px;
}
#countdown ul {
  margin: 5% 0 0 0;
  padding: 0;
  display: flex;
  gap: 5%;
}
#countdown ul li {
  flex: 25%;
  padding: 5%;
  margin: 0;
  list-style: none;
  background: #001f2f;
  border-radius: 5px;
}
#countdown ul li span {
  display: block;
  font-size: 3rem;
}