fish.css

@keyframes swim-across-screen-rtl {
    0% {
        right: -50vw;
    }

    100% {
        right: 150vw;
    }
}

@keyframes swim-across-screen-ltr {
    0% {
        left: -50vw;
    }

    100% {
        left: 150vw;
    }
}

@keyframes bob-up-and-down {
    0% {
        padding-top: 0px;
        padding-bottom: 0px;
    }

    50% {
        padding-top: 6px;
        padding-bottom: 6px;
    }

    100% {
        padding-top: 0px;
        padding-bottom: 0px;
    }
}

div.fish {
    position: fixed;
    z-index: -1;
    font-size: 1rem;
}

div.fish.tropical {
    animation-name: swim-across-screen-rtl, bob-up-and-down;
    animation-delay: 70s, 0s;
    animation-duration: 90s, 2s;
    animation-iteration-count: infinite, infinite;
    top: 10%;
    right: -50vw;
}

div.fish.blowfish {
    animation-name: swim-across-screen-ltr, bob-up-and-down;
    animation-delay: 100s, 0.2s;
    animation-duration: 140s, 4s;
    animation-iteration-count: 1, infinite;
    transform: scale(-1, 1);
    top: 22%;
    left: -50vw;
}

div.fish.school1.member1 {
    animation-name: swim-across-screen-rtl, bob-up-and-down;
    animation-delay: 10s, 0s;
    animation-duration: 38s, 1s;
    animation-iteration-count: infinite, infinite;
    animation-timing-function: ease-in-out, linear;
    bottom: 20%;
    right: -50vw;
}

div.fish.school1.member2 {
    animation-name: swim-across-screen-rtl, bob-up-and-down;
    animation-delay: 12s, 0.1s;
    animation-duration: 38s, 1s;
    animation-iteration-count: infinite, infinite;
    animation-timing-function: ease-out, linear;
    bottom: 22%;
    right: -50vw;
}

div.fish.school1.member3 {
    animation-name: swim-across-screen-rtl, bob-up-and-down;
    animation-delay: 10.2s, 0.2s;
    animation-duration: 38s, 1s;
    animation-iteration-count: infinite, infinite;
    animation-timing-function: ease-in-out, linear;
    bottom: 28%;
    right: -50vw;
}

div.fish.school1.member4 {
    animation-name: swim-across-screen-rtl, bob-up-and-down;
    animation-delay: 9.6s, 0.6s;
    animation-duration: 38s, 1.5s;
    animation-iteration-count: infinite, infinite;
    animation-timing-function: linear, linear;
    bottom: 15%;
    right: -50vw;
}