.birthday-container {
    position: fixed;
    top: 0;
    left: 0;
    width: 100vw;
    height: 100vh;
    pointer-events: none;
    z-index: 9999;
    overflow: hidden;
    contain: strict;
}

.birthday-cake {
    position: absolute;
    bottom: 2vh;
    left: 50vw;
    transform: translateX(-50%);
    font-size: 8rem;
    z-index: 50;
    filter: drop-shadow(0 0 10px rgba(255,255,255,0.4));
}

.birthday-cake img {
    height: 15vh;
    width: auto;
    object-fit: contain;
    max-height: 150px;
}

.birthday-symbol {
    position: absolute;
    bottom: -10vh; /* balloons rise from bottom */
    animation: birthday-rise linear infinite;
    font-size: 3rem;
    opacity: 0.95;
    z-index: 40;
}

.birthday-symbol img {
    width: 6vh;
    height: auto;
    max-width: 60px;
    object-fit: contain;
}

.birthday-confetti {
    position: absolute;
    top: -5vh;
    width: 10px;
    height: 10px;
    opacity: 0.9;
    animation: birthday-confetti-fall linear infinite;
    z-index: 30;
    /* Mix of circles and squares by using CSS variables or random in JS. For simplicity, we make all slightly rounded rectangles */
    border-radius: 2px;
}

@keyframes birthday-rise {
    0% { 
        transform: translateY(10vh) rotate(var(--start-rot, 0deg)); 
        opacity: 0; 
    }
    10% { 
        opacity: 1; 
    }
    90% {
        opacity: 1;
    }
    100% { 
        transform: translateY(-110vh) rotate(calc(var(--start-rot, 0deg) * -1)); 
        opacity: 0; 
    }
}

@keyframes birthday-confetti-fall {
    0% {
        transform: translateY(-5vh) rotateX(0deg) rotateY(0deg) rotateZ(0deg);
        opacity: 0;
    }
    5% {
        opacity: 1;
    }
    90% {
        opacity: 1;
    }
    100% {
        transform: translateY(105vh) rotateX(720deg) rotateY(360deg) rotateZ(180deg);
        opacity: 0;
    }
}