Модальное окно


<button id="modal-open" class="c-btn c-btn--primary">
  Открыть модальное окно
</button>
<div id="modal" class="c-modal">
  <div class="c-modal__back"></div>
  <div class="c-modal__window">
    <div id="modal-close" class="c-modal__close">
      <svg class="icon icon--close-cross" fill="currentColor">
        <use xlink:href="img/svg/sprite.svg#close-cross"></use>
      </svg>
    </div>
    <div class="c-modal__body">
      Тут содержимое.
    </div>
  </div>
</div>


.c-modal {
  --clr-modal-backdrop: rgba(196,196,196,.5);
  --clr-modal-window-back: var(--clr-sym-modal-window-back);
  --clr-modal-window-border: var(--clr-sym-modal-window-border);
  display: none;
  position: fixed;
  width: 100vw;
  height: 100vh;
  top: 0;
  left: 0;
  background-color: var(--clr-modal-backdrop);
  z-index: 1;
}
.c-modal__window {
  position: absolute;
  padding: 1.875rem 2.5rem;
  max-width: 28.625rem;
  background-color: var(--clr-modal-window-back);
  border-radius: 8px;
  border: 1px solid var(--clr-modal-window-border);
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}
.c-modal__close {
  position: absolute;
  top: 0.9375rem;
  right: 0.9375rem;
  cursor: pointer;
}