*{
  font-family: Avenir, sans-serif;
  font-size: 1em;
  text-align: center;
  margin: 0px;
  padding: 0px;
  box-sizing: border-box;
}
.conteneur-grid{
  display: grid;
  grid-template-columns: 1fr 2fr 1fr;
  grid-template-rows: 1fr minmax(150px, 2fr) 1fr;
  grid-template-areas: "gauche . ." "gauche . ." ". . .";
  border: 2px solid red;
  background-color: #DDD;
  margin: 10px;
}
.conteneur-grid > div{
  padding: 20px 0px;
  background-color: #ED8;
  border: 1px dashed black;
}
.g1{
    grid-area: gauche;
}
.g2{
    grid-column: gauche-start / 3;
    grid-row: gauche-end / 4;
}