style.css

@import url('https://fonts.googleapis.com/css2?family=Poppins:ital,wght@0,100;0,200;0,300;0,400;0,500;0,600;0,700;0,800;0,900;1,100;1,200;1,300;1,400;1,500;1,600;1,700;1,800;1,900&display=swap');

@keyframes fadeOut {
    from {
      opacity: 1;
    }
    to {
      opacity: 0;
    }
  }
  
.fade-out {
    animation: fadeOut 1s ease-in-out;
}

body {
    font-family: Poppins;
    margin: 0;
    padding: 0;
    min-height: 100vh;
    background: linear-gradient(180deg, rgba(180,247,238,1) 0%, rgba(211,176,242,1) 100%);
}

h1 {
    margin-top: 20px;
    text-align: center;
    
}

input {
    text-align: center;
    max-width: 200px;
}

#form {
    display: flex;
    flex-direction: row;
    justify-content: center;
}

h3 {
    font-weight: 400;
}

header {
    margin-top: 100px;
    margin-bottom: 20px;
}

.fade-out {
    animation: fadeOut 0.5s ease-out forwards;
}

@keyframes fadeOut {
    0% {
        opacity: 1;
    }
    100% {
        opacity: 0;
        display: none;
    }
}

.fade-in {
    animation: fadeIn 0.5s ease-in forwards;
}

@keyframes fadeIn {
    0% {
        opacity: 0;
        display: none;
    }
    100% {
        opacity: 1;
    }
}

#relogio {
    display: none;
    background: white;
    border-radius: 10px;
    padding: 15px;
    width: 500px;
    margin: auto;
    margin-top: 30px;
    box-shadow: 0px 0px 10px rgba(5, 22, 46, 0.180); /* deslocamento lateral - deslocamento vertical - espalhamento - cor*/
    text-align: center;
    font-size: 40px;
    font-weight: 600;
    letter-spacing: 1px;
}

@media only screen and (max-width: 600px) {
    body {
        text-align: center;
    }

    #relogio {
        width: 300px;
    }
}