foundry/Data/systems/dnd5e/templates/advancement/hit-points-flow.hbs

<form id="{{appId}}" data-level="{{level}}" data-id="{{advancement.id}}" data-type="{{type}}">
  <h3>{{{title}}}</h3>

  {{#if isFirstClassLevel}}

    <div>
      {{{localize "DND5E.AdvancementHitPointsMaxAtFirstLevel" max=dieValue}}}
      <input type="hidden" name="useMax" value="true" data-dtype="Boolean">
    </div>

  {{else}}

    <div class="rolls">
      <label class="averageLabel">
        <span>{{localize "DND5E.AdvancementHitPointsAverage"}}</span>
        <input class="averageCheckbox" type="checkbox" name="useAverage" {{checked data.useAverage}}>
      </label>
      <input class="rollResult" type="number" name="value" value="{{data.value}}" {{disabled data.useAverage}}>
      <button class="rollButton" type="button" name="roll" {{disabled data.useAverage}}>
        <i class="fas fa-dice-d20"></i> {{localize "DND5E.AdvancementHitPointsRollButton" die=hitDie}}
      </button>
    </div>

  {{/if}}
</form>