<form>
  <label for="amount">How many tickets? (You can buy 2-6 tickets)</label>
  <input id="amount" name="amount" type="number" min="2" max="6" value="4" />

  <label for="dep">Departure Date: (Whole year 2022 is acceptable)</label>
  <input id="dep" name="dep" type="date" min="2022-01-01" max="2022-12-31" value="2025-05-05" />

  <label for="ret">Return Date: (Whole year 2022 is acceptable)</label>
  <input id="ret" name="ret" type="date" min="2022-01-01" max="2022-12-31" />
</form>

label {
  display: block;
  margin-top: 1em;
}

input:in-range {
  background-color: palegreen;
}