Use .requiredclass with .form-labelor any custom element to indicate input's mandatory status:
Use .form-select-solidclass with .form-selectto set solid background style for a form select:
<select class="form-select" aria-label="Select example">
<option>Open this select menu</option>
<option value="1">One</option>
<option value="2">Two</option>
<option value="3">Three</option>
</select>
Use .form-rangeclass with .form-selectto set solid background style for a form select: