<p style="text-align: center;"><a href="#" class="modal-open" title="">open</a></p>
for demo create in your html this
<div class="container"></div>
<div data-supermodal ='1'>
<div class="modal-overlay modal_closed"></div>
<div class="modal modal_closed">
<header class="modal__header">
<a href="#" class="modal__close modal-close" title="Close">Close</a>
<h2>Enter</h2>
</header>
<main class="modal__content">
<div class="form-field">
<label for="name">Name:</label>
<input required class="input__default " type="text" id="name" name="name">
</div>
<div class="form-field">
<label>B-day:</label>
<input required type="number" class="input__date-birth birth-day"
name="name" placeholder="Day"> -
<input required type="number" class="input__date-birth birth-month"
name="name" placeholder="Mounth"> -
<input required type="number" class="input__date-birth birth-year"
name="name" placeholder="Ywar">
</div>
</main>
<footer class="modal__footer">
<button class="modal__cancel modal-cancel" title="Cancel">Cancel</button>
<button class="modal__save modal-save" title="Save">Save</button>
</footer>
</div>
</div>
<div data-supermodal ='2' >
<div class="modal-overlay modal_closed"></div>
<div class="modal modal_closed modal-close">
<header class="modal__header">
<a href="#" class="modal__close" title="Close">Close</a>
<h2>Video</h2>
</header>
<main class="modal__content">
<iframe width="550" height="235"
src="https://www.youtube.com/embed/HikrioqKxw4" frameborder="0"
allow="accelerometer; autoplay; encrypted-media; gyroscope;
picture-in-picture" allowfullscreen></iframe>
</main>
</div>
</div>
data-supermodelTitle = 'data-supermodelTitle' - title
data-supermodalContent="modalContent" - content
<div data-supermodal ='3' data-supermodelTitle =
'data-supermodelTitle' data-supermodalContent="modalContent">
<div class="modal-overlay modal_closed" ></div>
<div class="modal modal_closed">
<header class="modal__header">
<a href="#" class="modal__close" id="modal-close" title=""></a>
<h2></h2>
</header>
<main class="modal__content">
</main>
<footer class="modal__footer">
<button class="modal__cancel" title="Cancel"></button>
</footer>
</div>
</div>
PavelP