Андрей

function temp() {
    modal.style.display = "block";
}
btn.onclick = temp
btn2.onclick = temp

<input id="checkbox" type="checkbox" name="checkbox" required />

.grid {
  display: flex;
  flex-flow: row wrap;
  justify-content: space-between;
}

.grid::after {
  content: "";
  flex: auto;
}