<fieldset>
    <legend>Monster details</legend>

    <label for="height">Height (metres):</label>
    <input type="number" id="height" name="height"
           placeholder="10cm increments" step="0.1" />
    <span class="validity"></span>

    <label for="eyes">Number of eyes:</label>
    <input type="number" id="eyes" name="eyes"
           placeholder="Min: 10, max: 100"
           min="10" max="100" />
    <span class="validity"></span>

</fieldset>

Output