Exemplo de modal centralizado

by Rodrigo Portillo

HTML

<main class="pagina">
  <div class="box">
    <h1>Ai nessa box tem goteira...</h1>
    <button class="btn" onclick="modal(true)">
    Clica nimin... clica nimim....
    </button>
  </div>
</main>
<div class="modal">
  <div class="panel box">
    <div>
    Relou Uoldi
    </div>
    <button class="btn" onclick="modal(false)">
    Fechar
    </button>
  </div>
</div>

CSS

body{
  font-family: sans-serif;
}

.box{
  box-shadow: 0 .2rem .5rem rgba(0,0,0,.1);
  border-radius: .5rem;
  padding: 1rem;
  box-sizing: border-box;
  background-color: white;
}

.btn{
  box-shadow: 0 .1rem .1rem rgba(0,0,0,.2);
  border-radius: .2rem;
  padding: .2rem .5rem;
  box-sizing: border-box;
  border: none;
  background-color: #ccee22;
  border: 1px solid white;
}

.btn:active{
  box-shadow: 0 .01rem .01rem rgba(0,0,0,.3);
}

.modal{
  position: fixed;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
  display: flex;
  flex-direction: column;
  justify-content: center;
  backdrop-filter: blur(5px) brightness(.8);
  transition: all .3s;
  opacity: 0;
  pointer-events: none;
}

.modal .panel{
  margin: 0 auto;
  width: auto;
  transition: all .3s;
  opacity: 0;
  transform: scale(.8);
}

.modal.open{
  opacity: 1;
  pointer-events: all;
}
.modal.open .panel{
  opacity: 1;
  transform: scale(1);
}

JavaScript

function modal(open){
if(open){
document.querySelector(".modal").classList.add("open");
}else{
document.querySelector(".modal").classList.remove("open");
}
}