Cómo agregar Fade-In con la transición de la página

body {
    animation: fadeInAnimation ease 0.4s;
    animation-iteration-count: 1;
    animation-fill-mode: forwards;
}

@keyframes fadeInAnimation {
    0% {
        opacity: 0;
    }
    100% {
        opacity: 1;
     }
}
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