Bootstrap4のグリッドシステム v3からの変更点

/* Extra small devices: Phones (<768px) */
@media (max-width: 767px) {}
 
/* Small devices: Tablets (≥768px) */
@media (min-width: 768px) and (max-width: 991px) {}
 
/* Medium devices: Desktops (≥992px) */
@media (min-width: 992px) and (max-width: 1199px) {}
 
/* Large devices: Desktops (≥1200px) */
@media (min-width: 1200px) {}

/* Extra small devices: Phones (<576px) */
@media (max-width: 575px) {}
 
/* Small devices: Phablet (≥576px) */
@media (min-width: 576px) and (max-width: 767px) {}
 
/* Medium devices: Tablets (≥768px) */
@media (min-width: 768px) and (max-width: 991px) {}
 
/* Large devices: laptop (≥992px) */
@media (min-width: 992px) and (max-width: 1199px) {}
 
/* Extra Large devices: Desktops (≥1200px) */
@media (min-width: 1200px) {}

@media (min-width: 576px) {
  .container {
    max-width: 540px;
  }
}
@media (min-width: 768px) {
  .container {
    max-width: 720px;
  }
}
@media (min-width: 992px) {
  .container {
    max-width: 960px;
  }
}
@media (min-width: 1200px) {
  .container {
    max-width: 1140px;
  }
}