.search-expand {
  display: flex;
  max-width: 20rem;
  margin: 1rem auto;
  padding: 0.5rem;
}

.search-expand__input,
.search-expand__btn {
  height: 3rem;
  transition: width 0.25s ease, transform 0.25s ease, background 0.25s ease;
}

.search-expand__input {
  width: 3rem;
  border: none;
  border-radius: 1.5rem;
  box-shadow: 0 0 0 2px var(--color-dark) inset;
  padding: 0 0.75rem;
  background: transparent;
  appearance: none;
}

.search-expand__input:focus,
.search-expand__input:valid {
  width: 100%;
  background: #fff;
  box-shadow: 0 0 0 1px #ced4da inset;
  border-radius: 0.375rem 0 0 0.375rem;
}

.search-expand__btn {
  width: 3rem;
  border: none;
  border-radius: 0 0.75rem 0.75rem 0;
  background: var(--color-dark);
  color: #fff;
  cursor: pointer;
}

.search-expand__input:focus + .search-expand__btn,
.search-expand__input:valid + .search-expand__btn {
  width: auto;
  padding: 0 1rem;
  border-radius: 0 0.375rem 0.375rem 0;
}

.search-expand__input:invalid:not(:focus) + .search-expand__btn {
  cursor: pointer;
}