message: Updated: implemented the Numberinput component.
diff: }
  .Numberinput__form {
  + display: flex;
  position: relative;
  }
  .Numberinput__input {
  + flex-grow: 1;
  + flex-shrink: 0;
  display: block;
  - width: 100%;
  + width: 0;
  padding: 14px;
  font-size: 18px;
  background-color: var(--color-basic-white);
  border: 1px solid var(--color-basic-gray);
  - border-radius: 3px;
  + border-radius: 3px 0 0 3px;
  +}
  +
  +.Numberinput__handler {
  + user-select: none;
  + width: 50px;
  + border-radius: 0 3px 3px 0;
  + font-weight: 700;
  + color: var(--color-basic-lightGray);
  + border: solid 1px var(--color-basic-gray);
  + border-left: 0;
  + transition: opacity 0.24s linear 0.1s;
  + @apply --layout-column-stretch-center;
  +}
  +
  +.Numberinput__handler__button {
  + height: 50%;
  + outline: none;
  + @apply --layout-center-center;
  +}
  +
  +.Numberinput__handler__button:focus {
  + outline: none;
  +}
  +
  +.Numberinput__handler__button:hover {
  + height: 70%;
  + color: var(--color-text-anchorLight);
  + transition: all 0.1s linear;
  cursor: pointer;
  }
  +
  +.Numberinput__handler__button:active {
  + background-color: var(--color-basic-lightGray);
  + transition: all 0.1s linear;
  +}
  +
  +.Numberinput__handler__button:first-child {
  + border-bottom: solid 1px var(--color-basic-gray);
  +}
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