body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
}
header{
    background-color: #000000;
    color: white;
    padding: 12px;
    text-align: center;
}
.promo{
    background-image: url(../images/iphone.jpg);
    background-size: 100%;
    opacity: 0.5;
    height: 300px;
    display: flex;
    align-items: center;
    justify-content: center;    
    font-size: 4em;
    text-shadow: 3px 3px 2px black;
    color: yellow;
}
.description{
    display: flex;
    flex-wrap: wrap;
    gap: 12px;
    padding: 20px;
    justify-content: center;
}
.feature{
    flex: 1 1 200px; /*flex-grow, flex-shrink, flex-basis*/
    border: 1px solid #b1b2b3;
    padding: 12px;
    border-radius: 8px;
}
.action{
    background-color: #53ed68;
    color: white;
    padding: 30px;
    text-align: center;
}
.action button{
    padding: 15px 30px;
    border-radius: 10px;
}
button:hover{
    background-color: #3bd8ed;
}