@media (min-width: 0) {
  .com-b .back-title {
    font-size: 45px;
  }
  .com-b .c-box .c-item .c-title {
    font-size: 18px;
  }
}
@media (min-width: 768px) {
  .com-b .back-title {
    font-size: 60px;
  }
}
@media (min-width: 992px) {
  .com-b .back-title {
    font-size: 100px;
  }
}
@media (min-width: 1200px) {
  .com-b .c-box .c-item .c-title {
    font-size: 20px;
  }
}