.navbar,
.navbar-default {
  box-shadow: none;
}

.card{
  margin-bottom: 2rem;
}
.card img {
  width: 100%;
  height: 260px; /* default (mobile) */
  object-fit: cover;
}

@media (min-width: 768px) { /* tablet */
  .card img {
    height: 150px;
  }
}

@media (min-width: 1200px) { /* big screen */
  .card img {
    height: 260px;
  }
}