style.css

*,
*::before,
*::after {
  box-sizing: border-box;
  font-family: Play, Verdana, Geneva, Tahoma, sans-serif;
  font-size: 1.1rem;
  line-height: 1.5rem;
}

body {
  padding: 0;
  margin: 1vh 0;
  display: flex;
  flex-flow: column nowrap;
  justify-content: center;
  align-items: center;
  width: 100vw;
  background-color: #333;
}

.reference {
  color: rgb(195, 195, 195);
  font-size: 1.5rem;
  margin: 5px;
  border: 5px solid red;
  padding: 5px;
  text-align: center;
}

.reference a {
  color: red;
  font-size: 1.5rem;
}

.reference a:hover {
  text-decoration: underline;
}

.container {
  width: 800px;
  max-width: 80%;
  background-color: rgb(195, 195, 195);
  padding: 10px;
  border-radius: 5px;
  box-shadow: 0 0 10px 2px;
}

.btn-grid {
  display: grid;
  grid-template-columns: repeat(2, auto);
  gap: 10px;
  margin-top: 20px;
}

.btn {
  background-color: rgb(95, 95, 95);
  border: 1px solid;
  border-radius: 5px;
  padding: 5px 10px;
  color: rgb(210, 210, 210);
  outline: none;
}

.btn:hover {
  background-color: rgb(195, 195, 195);
  border-color: black;
  color: black;
  cursor: pointer;
  transition: 0.5s;
}

/* Introductory page */

#intro-container {
  display: flex;
  flex-direction: column;
  align-items: center;
}

a {
  text-decoration: none;
}