www/static/css/errors.css

html,
body {
    height: 100%;
    overflow: hidden;
}

.error-page {
    display: flex;
    align-items: center;
    justify-content: center;
    text-align: center;
    height: 100%;
    font-family: Arial, "Helvetica Neue", Helvetica, sans-serif;
}

.error-page h1 {
    font-size: 30vh;
    font-weight: bold;
    position: relative;
    margin: -8vh 0 0;
    padding: 0;
}

.error-page h1:after {
    content: attr(data-h1);
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    color: transparent;
    /* webkit only for graceful degradation to IE */
    background: -webkit-repeating-linear-gradient(
        -45deg,
        #71b7e6,
        #69a6ce,
        #b98acc,
        #ee8176,
        #b98acc,
        #69a6ce,
        #9b59b6
    );
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-size: 400%;
    text-shadow: 1px 1px 2px transparentize(#fff, 0.75);
    animation: animateTextBackground 10s ease-in-out infinite;
}

.error-page h1 + p {
    color: #d6d6d6;
    font-size: 8vh;
    font-weight: bold;
    line-height: 10vh;
    max-width: 600px;
    position: relative;
}

.error-page h1 + p:after {
    content: attr(data-p);
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    color: transparent;
    text-shadow: 1px 1px 2px transparentize(#fff, 0.5);
    -webkit-background-clip: text;
    -moz-background-clip: text;
    background-clip: text;
}

#tsparticles {
    position: fixed;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
}

@keyframes animateTextBackground {
    0% {
        background-position: 0 0;
    }

    25% {
        background-position: 100% 0;
    }

    50% {
        background-position: 100% 100%;
    }

    75% {
        background-position: 0 100%;
    }

    100% {
        background-position: 0 0;
    }
}

@media (max-width: 767px) {
    .error-page h1 {
        font-size: 32vw;
    }

    .error-page h1 + p {
        font-size: 8vw;
        line-height: 10vw;
        max-width: 70vw;
    }
}

a.back {
    position: fixed;
    right: 40px;
    bottom: 40px;
    background: -webkit-repeating-linear-gradient(-45deg, #71b7e6, #69a6ce, #b98acc, #ee8176);
    border-radius: 5px;
    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.2);
    color: #fff;
    font-size: 16px;
    font-weight: bold;
    line-height: 24px;
    padding: 15px 30px;
    text-decoration: none;
    transition: 0.25s all ease-in-out;
}

a.back:hover {
    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.4);
}