body {
  font-family: Arial, sans-serif;
  margin: 20px;
  background: #f7f7f7;
}

h1, h2 {
  color: #333;
}

.toolbar {
  margin-bottom: 20px;
}

#plan {
  width: 100%;
  height: 500px;
  border: 2px dashed #aaa;
  margin-bottom: 20px;
  position: relative;
  background: repeating-linear-gradient(
    0deg,
    #eee,
    #eee 20px,
    #fff 20px,
    #fff 40px
  ),
  repeating-linear-gradient(
    90deg,
    #eee,
    #eee 20px,
    #fff 20px,
    #fff 40px
  );
}

.objet {
  position: absolute;
  border: 1px solid #444;
  background: #ddd;
  padding: 5px;
  cursor: move;
  user-select: none;
  min-width: 60px;
  text-align: center;
  border-radius: 5px;
}