:in-range

/* Selects any <input>, but only when it has a range */
/* specified, and its value is inside that range */
input:in-range {
  background-color: rgba(0, 255, 0, 0.25);
}

:in-range

<form action="" id="form1">
  <ul>Values between 1 and 10 are valid.
?   <li>
???   <input id="value1" name="value1" type="number" placeholder="1 to 10" min="1" max="10" value="12">
???   <label for="value1">Your value is </label>
?   </li>
  </ul>
</form>

li {
? list-style: none;
? margin-bottom: 1em;
}

input {
? border: 1px solid black;
}

input:in-range {
? background-color: rgba(0, 255, 0, 0.25);
}

input:out-of-range {
? background-color: rgba(255, 0, 0, 0.25);
? border: 2px solid red;
}

input:in-range + label::after {
? content:' OK';
}

input:out-of-range + label::after {
? content:'out of range!';
}