*, *::before, *::after {
  box-sizing: border-box;
}

body {
  height: 100vh;
  margin: 0;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
}

section.markers {
  display: grid;
  grid-template-columns: repeat(7, 10vmin);
  grid-gap: 1vmin;
  margin-bottom: 1vmin;
}

section.markers div {
  border-top: 5vmin solid lightgrey;
  border-left: 5vmin solid transparent;
  border-right: 5vmin solid transparent;
}

section.markers div:hover {
  border-top-color: grey;
}

section.board {
  display: grid;
  grid-template-columns: repeat(7, 10vmin);
  grid-template-rows: repeat(6, 10vmin);
  grid-gap: 1vmin;
}

section.board div {
  border-radius: 50%;
  border: 1px solid grey;
}