library / backgrounds / 1-urban-downpour-with-lightning
live - 60fps 1920 x 1080
1-urban-downpour-with-lightning.html - self-contained
<!DOCTYPE html>
<html>
<head>
<title>1. Urban Downpour with Lightning</title>
<style>
    :root {
        --rain-bg: #11141d;
        --drop-color: #cbd5e1;
    }
    body {
        margin: 0;
        height: 100vh;
        background-color: var(--rain-bg);
        overflow: hidden;
        position: relative;
    }
    .rain-container {
        position: absolute;
        top: 0; left: 0;
        width: 100%; height: 100%;
    }
    .rain-drop {
        position: absolute;
        bottom: 100%;
        width: 2px;
        background: linear-gradient(to top, transparent, var(--drop-color));
        animation: fall 10s infinite linear;
    }
    /* Far layer - slower, smaller, more transparent */
    .rain-drop.back {
        opacity: 0.4;
        height: 30px;
        animation-duration: 2s;
        animation-timing-function: linear;
    }
    /* Mid layer - standard */
    .rain-drop.mid {
        opacity: 0.6;
        height: 50px;
        animation-duration: 1.2s;
        animation-timing-function: linear;
    }
    /* Near layer - faster, larger, more opaque */
    .rain-drop.front {
        opacity: 1;
        height: 80px;
        animation-duration: 0.7s;
        animation-timing-function: linear;
    }
    @keyframes fall {
        from { transform: translateY(0vh); }
        to { transform: translateY(110vh); }
    }
    .splash {
        position: absolute;
        bottom: 0;
        width: 4px;
        height: 4px;
        border-radius: 50%;
        background-color: var(--drop-color);
        opacity: 0;
        transform: scale(0);
        animation: splash-up 10s infinite ease-out;
    }
    @keyframes splash-up {
        0% { opacity: 0; transform: scale(0) translateY(0); }
        2% { opacity: 1; transform: scale(1) translateY(-10px); } /* Initial impact */
        5% { opacity: 0; transform: scale(1.5, 0.5) translateY(-50px); } /* Disperse */
        100% { opacity: 0; }
    }
    /* Lightning Flash Effect */
    .lightning {
        position: absolute;
        top: 0; left: 0;
        width: 100%; height: 100%;
        background: radial-gradient(circle at 50% 0%, white, transparent 40%);
        opacity: 0;
        animation: flash 10s infinite step-end;
    }
    @keyframes flash {
        0%, 94%, 100% { opacity: 0; }
        94.1% { opacity: 0.6; }
        94.2% { opacity: 0.1; }
        94.3% { opacity: 0.8; }
        94.6% { opacity: 0; }
    }
</style>
</head>
<body>
    <div class="lightning"></div>
    <div class="rain-container" id="rainContainer"></div>
<script>
    const container = document.getElementById('rainContainer');
    const totalDrops = 400;

    for (let i = 0; i < totalDrops; i++) {
        const drop = document.createElement('div');
        const splash = document.createElement('div');
        const layer = Math.random();
        
        let layerClass = 'front';
        if (layer < 0.33) layerClass = 'back';
        else if (layer < 0.66) layerClass = 'mid';

        drop.className = `rain-drop ${layerClass}`;
        splash.className = 'splash';

        const leftPosition = `${Math.random() * 105 - 5}%`; // -5 to 105 to cover edges
        drop.style.left = leftPosition;
        splash.style.left = leftPosition;

        const delay = Math.random() * -10; // Use negative delay to start immediately
        drop.style.animationDelay = `${delay}s`;
        
        // Match splash delay to the corresponding drop duration
        const dropDuration = parseFloat(drop.style.animationDuration || '0.7s');
        splash.style.animationDelay = `${delay + dropDuration}s`;

        container.appendChild(drop);
        container.appendChild(splash);
    }
</script>
</body>
</html>

About this animation

Atmospheric rain with lightning effects.

Under the hood

Canvas Particle Physics & CSS Flashes

The rain effect is driven by an HTML5 that calculates downward velocity vectors for hundreds of stroke lines. To optimize performance, the lightning flashes are handled via a separate CSS animation adjusting background overlay opacity, preventing the canvas from needing to recompute full-screen fillRect paint operations.

Source Code
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