* {
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

html,
body {
  margin: 0;
  border: 0;
  padding: 0;
  background-color: #fff;
}

main {
  margin: auto;
  width: 80%;
  padding: 20px;
}

main>h1 {
  text-align: center;
  font-size: 3.5em;
}

table,
th,
td {
  border: 1px solid black;
  border-collapse: collapse;
  padding: 0.5em;
}

th {
  text-align: left;
}

#mats>div {
  display: flex;
  justify-content: center;
}

#mats>div>div {
  border: 1px solid slategray;
  background-color: lightgrey;
  border-radius: .25em;
  height: 5em;
  width: 5em;
  display: flex;
  align-items: center;
  justify-content: center;
  margin: .25em;
}

img {
  width: 80%;
  padding: 1em 2em;
}