MOT,
<!DOCTYPE html>
<html>
<head>
<style>
#modal {
width: 50%;
height: 70%;
background: linear-gradient(white, #216558);
left: 0;
top: -180%;
bottom: 0;
right: 0;
margin: auto;
border-radius: 25px;
padding: 15px;
opacity: .1;
position: fixed;
transition: top .5s linear 1s, opacity 2s;
}
#checkbox:checked ~ #modal {
transition: top .5s linear .3s, opacity 1s .8s;
top: 0;
opacity: 1;
}
</style>
</head>
<body>
<input type="checkbox" id="checkbox">
<label for="checkbox">Открыть</label>
<div id="modal">
<span>типо контент</span><br>
<label for="checkbox">Закрыть</label>
</div>
</body>
</html>