CHEAP ──────────────────────── STYLIZED ──────────────────────── REALISTIC
CSS gradient blob         SVG filter + layered opacity        WebGL particles
Single div animation      3-5 layers with parallax            Fluid simulation
Linear easing             Cubic-bezier + varied timing        Physics engine

<div class="atmosphere-container">
  <!-- BACK clouds (behind content) -->
  <div class="clouds clouds--back"></div>

  <!-- Content sits in the middle -->
  <main class="content">
    <div class="card">Your content here</div>
  </main>

  <!-- FRONT clouds (in front of content, but transparent) -->
  <div class="clouds clouds--front"></div>
</div>

.atmosphere-container {
  position: relative;
  isolation: isolate; /* Creates stacking context */
}

.clouds {
  position: absolute;
  inset: 0;
  pointer-events: none; /* CRITICAL: Let clicks through */
  filter: url(#cloud-cumulus);
}

.clouds--back {
  z-index: -1;
  opacity: 0.3;
  transform: scale(1.5);
  animation: drift 120s linear infinite;
}

.content {
  position: relative;
  z-index: 1;
}

.clouds--front {
  z-index: 2;
  opacity: 0.12; /* LOW opacity so content is readable */
  transform: scale(0.8);
  animation: drift 50s linear infinite reverse;

  /* Optional: Mask to clear space around content */
  mask-image: linear-gradient(
    to bottom,
    black 0%,
    transparent 30%,
    transparent 70%,
    black 100%
  );
}

.clouds--front {
  mix-blend-mode: soft-light; /* Blends naturally with content */
  opacity: 0.25;
}

/* Or for white clouds on dark backgrounds */
.clouds--front {
  mix-blend-mode: screen;
  opacity: 0.15;
}

/* Add subtle backdrop to cards so text is always readable */
.card {
  background: rgba(255, 255, 255, 0.85);
  backdrop-filter: blur(4px); /* Blurs back clouds for extra depth */
}

<svg width="0" height="0">
  <defs>
    <filter id="atmosphere" x="-50%" y="-50%" width="200%" height="200%">
      <!-- 1. Generate noise texture -->
      <feTurbulence
        type="fractalNoise"      <!-- or "turbulence" for water -->
        baseFrequency="0.01"     <!-- Lower = larger shapes -->
        numOctaves="4"           <!-- 3-5 for good detail -->
        seed="1"                 <!-- Change for variation -->
        result="noise"
      />

      <!-- 2. Distort the source -->
      <feDisplacementMap
        in="SourceGraphic"
        in2="noise"
        scale="30"               <!-- Distortion intensity -->
        xChannelSelector="R"
        yChannelSelector="G"
        result="displaced"
      />

      <!-- 3. Soften edges -->
      <feGaussianBlur
        in="displaced"
        stdDeviation="2"
        result="blurred"
      />

      <!-- 4. Add lighting (optional) -->
      <feDiffuseLighting
        in="noise"
        lighting-color="white"
        surfaceScale="2"
        result="lit"
      >
        <feDistantLight azimuth="45" elevation="60" />
      </feDiffuseLighting>

      <!-- 5. Composite layers -->
      <feComposite in="blurred" in2="lit" operator="multiply" />
    </filter>
  </defs>
</svg>

.cloud-layer {
  position: absolute;
  inset: 0;
  background: radial-gradient(
    ellipse 200% 100% at 50% 100%,
    rgba(255, 255, 255, 0.9) 0%,
    transparent 70%
  );
  filter: url(#cloud-filter);
}

/* Layer hierarchy: back → front */
.cloud-back {
  opacity: 0.3;
  transform: scale(1.5);
  animation: drift 120s linear infinite;
}

.cloud-mid {
  opacity: 0.5;
  transform: scale(1.2);
  animation: drift 80s linear infinite;
}

.cloud-front {
  opacity: 0.7;
  transform: scale(1);
  animation: drift 50s linear infinite;
}

@keyframes drift {
  from { transform: translateX(-10%); }
  to { transform: translateX(10%); }
}

:root {
  /* Daylight clouds */
  --cloud-white: rgba(255, 255, 255, 0.9);
  --cloud-highlight: rgba(255, 250, 240, 1);
  --cloud-shadow: rgba(180, 190, 210, 0.6);

  /* Sunset clouds */
  --cloud-gold: rgba(255, 200, 100, 0.8);
  --cloud-pink: rgba(255, 150, 180, 0.7);
  --cloud-purple: rgba(180, 100, 200, 0.5);

  /* Storm clouds */
  --storm-dark: rgba(60, 70, 90, 0.9);
  --storm-purple: rgba(80, 60, 100, 0.7);
  --storm-highlight: rgba(200, 210, 230, 0.4);
}

<!-- WATER uses type="turbulence" NOT fractalNoise -->
<feTurbulence
  type="turbulence"
  baseFrequency="0.01 0.03"  <!-- X << Y for horizontal waves -->
  numOctaves="3"
  result="waves"
/>

<svg viewBox="0 0 1440 320" preserveAspectRatio="none">
  <defs>
    <filter id="wave-distort">
      <feTurbulence
        type="turbulence"
        baseFrequency="0.01 0.02"
        numOctaves="3"
        result="turbulence"
      >
        <animate
          attributeName="baseFrequency"
          dur="20s"
          values="0.01 0.02; 0.015 0.025; 0.01 0.02"
          repeatCount="indefinite"
        />
      </feTurbulence>
      <feDisplacementMap
        in="SourceGraphic"
        in2="turbulence"
        scale="20"
        xChannelSelector="R"
        yChannelSelector="G"
      />
    </filter>
  </defs>

  <path
    fill="var(--ocean-color)"
    filter="url(#wave-distort)"
    d="M0,160 C360,220 720,100 1080,180 C1260,220 1380,140 1440,160 L1440,320 L0,320 Z"
  >
    <animate
      attributeName="d"
      dur="10s"
      repeatCount="indefinite"
      values="
        M0,160 C360,220 720,100 1080,180 C1260,220 1380,140 1440,160 L1440,320 L0,320 Z;
        M0,180 C360,120 720,200 1080,140 C1260,100 1380,180 1440,140 L1440,320 L0,320 Z;
        M0,160 C360,220 720,100 1080,180 C1260,220 1380,140 1440,160 L1440,320 L0,320 Z
      "
    />
  </path>
</svg>

:root {
  /* Deep ocean */
  --ocean-deep: #0c4a6e;
  --ocean-mid: #0369a1;
  --ocean-surface: #38bdf8;
  --ocean-foam: rgba(255, 255, 255, 0.8);

  /* Tropical */
  --tropical-deep: #047857;
  --tropical-mid: #10b981;
  --tropical-surface: #6ee7b7;

  /* Stormy */
  --stormy-deep: #1e3a5f;
  --stormy-mid: #334155;
  --stormy-surface: #64748b;

  /* Sunset reflection */
  --sunset-water: linear-gradient(
    180deg,
    rgba(251, 146, 60, 0.4) 0%,
    rgba(14, 165, 233, 0.6) 50%,
    #0c4a6e 100%
  );
}

<svg viewBox="0 0 100 200" class="lightning">
  <defs>
    <filter id="lightning-glow" x="-50%" y="-50%" width="200%" height="200%">
      <feGaussianBlur stdDeviation="3" result="blur" />
      <feMerge>
        <feMergeNode in="blur" />
        <feMergeNode in="SourceGraphic" />
      </feMerge>
    </filter>
  </defs>

  <path
    class="bolt"
    d="M50,0 L45,40 L55,45 L40,90 L60,95 L35,150 L70,100 L50,95 L65,50 L45,45 L60,10 Z"
    fill="none"
    stroke="white"
    stroke-width="2"
    filter="url(#lightning-glow)"
  />
</svg>

.lightning {
  position: absolute;
  pointer-events: none;
  opacity: 0;
}

.bolt {
  stroke-dasharray: 500;
  stroke-dashoffset: 500;
}

.lightning.flash {
  animation: lightning-flash 0.5s ease-out forwards;
}

.lightning.flash .bolt {
  animation: bolt-draw 0.15s ease-out forwards;
}

@keyframes lightning-flash {
  0% { opacity: 0; }
  10% { opacity: 1; }
  20% { opacity: 0.5; }
  30% { opacity: 1; }
  100% { opacity: 0; }
}

@keyframes bolt-draw {
  to { stroke-dashoffset: 0; }
}

.lightning-flash-overlay {
  position: fixed;
  inset: 0;
  background: rgba(255, 255, 255, 0);
  pointer-events: none;
  z-index: 1000;
}

.lightning-flash-overlay.active {
  animation: screen-flash 0.3s ease-out;
}

@keyframes screen-flash {
  0% { background: rgba(255, 255, 255, 0); }
  10% { background: rgba(200, 220, 255, 0.4); }
  20% { background: rgba(255, 255, 255, 0); }
  30% { background: rgba(200, 220, 255, 0.2); }
  100% { background: rgba(255, 255, 255, 0); }
}

function generateLightningPath(startX, startY, endY, segments = 8) {
  let path = `M${startX},${startY}`;
  let x = startX;
  let y = startY;
  const segmentHeight = (endY - startY) / segments;

  for (let i = 0; i < segments; i++) {
    const jitter = (Math.random() - 0.5) * 30;
    x += jitter;
    y += segmentHeight;
    path += ` L${x},${y}`;

    // Random branch (20% chance)
    if (Math.random() < 0.2) {
      const branchX = x + (Math.random() - 0.5) * 40;
      const branchY = y + segmentHeight * 0.5;
      path += ` M${x},${y} L${branchX},${branchY} M${x},${y}`;
    }
  }

  return path;
}

.rain-container {
  position: absolute;
  inset: 0;
  overflow: hidden;
  pointer-events: none;
}

.raindrop {
  position: absolute;
  width: 2px;
  background: linear-gradient(
    180deg,
    transparent 0%,
    rgba(174, 194, 224, 0.5) 50%,
    rgba(174, 194, 224, 0.8) 100%
  );
  border-radius: 0 0 2px 2px;
  animation: rain-fall var(--fall-duration) linear infinite;
  animation-delay: var(--delay);
  left: var(--x);
  height: var(--length);
  opacity: var(--opacity);
}

@keyframes rain-fall {
  0% {
    transform: translateY(-100vh);
  }
  100% {
    transform: translateY(100vh);
  }
}

function createRain(container, dropCount = 100) {
  for (let i = 0; i < dropCount; i++) {
    const drop = document.createElement('div');
    drop.className = 'raindrop';
    drop.style.setProperty('--x', `${Math.random() * 100}%`);
    drop.style.setProperty('--delay', `${Math.random() * 2}s`);
    drop.style.setProperty('--fall-duration', `${0.5 + Math.random() * 0.5}s`);
    drop.style.setProperty('--length', `${15 + Math.random() * 20}px`);
    drop.style.setProperty('--opacity', `${0.3 + Math.random() * 0.5}`);
    container.appendChild(drop);
  }
}

/* Light drizzle */
.rain-light {
  --drop-count: 50;
  --fall-duration-base: 1.2s;
  --drop-opacity: 0.3;
}

/* Moderate rain */
.rain-moderate {
  --drop-count: 150;
  --fall-duration-base: 0.8s;
  --drop-opacity: 0.5;
}

/* Heavy downpour */
.rain-heavy {
  --drop-count: 300;
  --fall-duration-base: 0.5s;
  --drop-opacity: 0.7;
}

.raindrop.windy {
  animation: rain-fall-diagonal var(--fall-duration) linear infinite;
}

@keyframes rain-fall-diagonal {
  0% {
    transform: translate(-50vw, -100vh) rotate(15deg);
  }
  100% {
    transform: translate(50vw, 100vh) rotate(15deg);
  }
}

.fog-container {
  position: absolute;
  inset: 0;
  overflow: hidden;
  pointer-events: none;
}

.fog-layer {
  position: absolute;
  width: 200%;
  height: 100%;
  background: url("data:image/svg+xml,...") repeat-x;
  opacity: 0.3;
  filter: url(#fog-filter);
}

.fog-back {
  animation: fog-drift 60s linear infinite;
  opacity: 0.2;
  transform: scale(1.5);
}

.fog-mid {
  animation: fog-drift 40s linear infinite reverse;
  opacity: 0.3;
  transform: scale(1.2);
}

.fog-front {
  animation: fog-drift 25s linear infinite;
  opacity: 0.4;
}

@keyframes fog-drift {
  from { transform: translateX(-50%); }
  to { transform: translateX(0%); }
}

<filter id="fog-filter" x="-50%" y="-50%" width="200%" height="200%">
  <feTurbulence
    type="fractalNoise"
    baseFrequency="0.003"
    numOctaves="4"
    seed="5"
    result="noise"
  />
  <feGaussianBlur in="noise" stdDeviation="20" result="blur" />
  <feColorMatrix
    type="matrix"
    values="1 0 0 0 0
            0 1 0 0 0
            0 0 1 0 0
            0 0 0 0.5 0"
    result="faded"
  />
</filter>