duration_element.css in Duration Field 3.0.x

.form-type-duration .duration-inner-wrapper {
  display: -webkit-box;
  display: -moz-box;
  display: -ms-flexbox;
  display: -webkit-flex;
  display: flex;
  -webkit-flex-wrap: wrap;
  -moz-flex-wrap: wrap;
  -ms-flex-wrap: wrap;
  flex-wrap: wrap;
  -webkit-justify-content: flex-start;
  -moz-justify-content: flex-start;
  -ms-justify-content: flex-start;
  justify-content: flex-start;
  -ms-flex-pack: start;
  margin: 0 -5px;
}
.form-type-duration .duration-inner-wrapper .form-type-number {
  padding: 0 5px;
  width: 5em;
}
.form-type-duration .duration-inner-wrapper .form-type-number input {
  box-sizing: border-box;
  width: 100%;
}