* {
    box-sizing: border-box;
}

body {
    margin: 0;
}

/* background */

.container {
    height: 100vh;

    background: linear-gradient(180deg, #0a0a2a, #1b3c73);

    display: flex;
    justify-content: center;
    align-items: center;

    position: relative;
    overflow: hidden;

    transition: background 6s;

}

.container:hover {
    background: linear-gradient(180deg, #3a1c71, #d76d77, #ffaf7b);
}

/* bubbles */

.bubble {
    position: absolute;

    border: 2px solid white;
    border-radius: 100%;

    background: transparent;

    transition: transform 0.3s;
}


.bubble:hover {
    transform: scale(1.3);
}

.b1 {
    width: 30px;
    height: 30px;
    left: 10%;
    bottom: -40px;
    animation: rise 10s infinite linear;
}

.b2 {
    width: 20px;
    height: 20px;
    left: 30%;
    bottom: -60px;
    animation: rise 4s infinite linear;
}

.b3 {
    width: 40px;
    height: 40px;
    left: 50%;
    bottom: -50px;
    animation: rise 15s infinite linear;
}

.b4 {
    width: 25px;
    height: 25px;
    left: 70%;
    bottom: -60px;
    animation: rise 16s infinite linear;
}

.b5 {
    width: 35px;
    height: 35px;
    left: 85%;
    bottom: -50px;
    animation: rise 11s infinite linear;
}

.b6 {
    width: 18px;
    height: 18px;
    left: 5%;
    bottom: -50px;
    animation: rise 9s infinite linear;
}

.b7 {
    width: 32px;
    height: 32px;
    left: 15%;
    bottom: -70px;
    animation: rise 19s infinite linear;
}

.b8 {
    width: 22px;
    height: 22px;
    left: 25%;
    bottom: -60px;
    animation: rise 13s infinite linear;
}

.b9 {
    width: 28px;
    height: 28px;
    left: 40%;
    bottom: -50px;
    animation: rise 12s infinite linear;
}

.b10 {
    width: 20px;
    height: 20px;
    left: 60%;
    bottom: -80px;
    animation: rise 6s infinite linear;
}

.b11 {
    width: 35px;
    height: 35px;
    left: 65%;
    bottom: -60px;
    animation: rise 14s infinite linear;
}

.b12 {
    width: 16px;
    height: 16px;
    left: 75%;
    bottom: -50px;
    animation: rise 5s infinite linear;
}

.b13 {
    width: 26px;
    height: 26px;
    left: 80%;
    bottom: -70px;
    animation: rise 10s infinite linear;
}

.b14 {
    width: 30px;
    height: 30px;
    left: 90%;
    bottom: -60px;
    animation: rise 7s infinite linear;
}

.b15 {
    width: 24px;
    height: 24px;
    left: 95%;
    bottom: -80px;
    animation: rise 6s infinite linear;
}

@keyframes rise {

    0% {
        bottom: -60px;
    }

    100% {
        bottom: 110vh;
    }

}