.tableau {
  margin: 4em; 
  margin-bottom: 2em;
  margin-top: -2em;
}

table {
  border: 1px solid black;
  border-spacing: 0;
  border-collapse: collapse;
}

thead {
  border-bottom: 2px solid black;
}

tr:nth-child(even) {
  background-color: rgb(228, 240, 245);
}