discourse/app/assets/stylesheets/common/components/date-time-input.scss

.d-date-time-input {
  display: flex;
  align-items: center;
  border: 1px solid $primary-low;
  box-sizing: border-box;
  position: relative;
  flex: 1;

  .date-picker,
  .fields {
    border: 0;
  }

  .d-date-time-input {
    margin-left: auto;
  }
}