Best Animated Backgrounds in CSS

<div class="nav" id="nav">
  <div class="nav-dot active" data-section="0"></div>
  <div class="nav-dot" data-section="1"></div>
  <div class="nav-dot" data-section="2"></div>
  <div class="nav-dot" data-section="3"></div>
  <div class="nav-dot" data-section="4"></div>
  <div class="nav-dot" data-section="5"></div>
  <div class="nav-dot" data-section="6"></div>
  <div class="nav-dot" data-section="7"></div>
</div>

<section class="section bg-gradient-wave">
  <div class="content">
    <h2>Gradient Wave</h2>
    <p>Smooth color-shifting gradient with purple and pink tones that flow like waves across the screen.</p>
  </div>
</section>

<section class="section bg-floating-circles">
  <div class="circle"></div>
  <div class="circle"></div>
  <div class="circle"></div>
  <div class="circle"></div>
  <div class="circle"></div>
  <div class="content">
    <h2>Floating Circles</h2>
    <p>Gentle bubbles rise from the bottom, creating a dreamy pink gradient atmosphere.</p>
  </div>
</section>

<section class="section bg-particle-stars">
  <div class="content">
    <h2>Particle Stars</h2>
    <p>Twinkling stars in a deep ocean-blue gradient, perfect for a cosmic feel.</p>
  </div>
</section>

<section class="section bg-mesh">
  <div class="mesh-layer"></div>
  <div class="content">
    <h2>Mesh Gradient</h2>
    <p>Modern mesh gradient with moving colored orbs in warm sunset tones.</p>
  </div>
</section>

<section class="section bg-waves">
  <div class="wave"></div>
  <div class="wave"></div>
  <div class="wave"></div>
  <div class="content">
    <h2>Wave Animation</h2>
    <p>Flowing ocean waves in bright cyan colors, creating a tranquil seaside vibe.</p>
  </div>
</section>

<section class="section bg-matrix">
  <div class="content">
    <h2>Matrix Rain</h2>
    <p>Digital rain effect with green characters falling, inspired by The Matrix.</p>
  </div>
</section>

<section class="section bg-aurora">
  <div class="aurora"></div>
  <div class="aurora" style="animation-delay: -10s;"></div>
  <div class="content">
    <h2>Aurora Borealis</h2>
    <p>Northern lights effect with flowing colorful ribbons across a dark night sky.</p>
  </div>
</section>

<section class="section bg-geometric">
  <div class="geometric-shape"></div>
  <div class="geometric-shape"></div>
  <div class="content">
    <h2>Geometric Pattern</h2>
    <p>Rotating 3D shapes with vibrant pink-red gradient background.</p>
  </div>
</section>

  * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }

        body {
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
            overflow-x: hidden;
        }

        .section {
            min-height: 100vh;
            display: flex;
            justify-content: center;
            align-items: center;
            position: relative;
            overflow: hidden;
        }

        .content {
            position: relative;
            z-index: 10;
            text-align: center;
            color: white;
            padding: 40px;
            background: rgba(0, 0, 0, 0.3);
            border-radius: 20px;
            backdrop-filter: blur(10px);
            max-width: 600px;
        }

        .content h2 {
            font-size: 3rem;
            margin-bottom: 20px;
            font-weight: 300;
            text-shadow: 0 2px 10px rgba(0, 0, 0, 0.3);
        }

        .content p {
            font-size: 1.2rem;
            opacity: 0.9;
            line-height: 1.6;
        }

        /* Background 1: Gradient Wave */
        .bg-gradient-wave {
            background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
            animation: gradientShift 8s ease infinite;
            background-size: 200% 200%;
        }

        @keyframes gradientShift {
            0%, 100% { background-position: 0% 50%; }
            50% { background-position: 100% 50%; }
        }

        /* Background 2: Floating Circles */
        .bg-floating-circles {
            background: linear-gradient(135deg, #f093fb 0%, #f5576c 100%);
        }

        .circle {
            position: absolute;
            border-radius: 50%;
            background: rgba(255, 255, 255, 0.1);
            animation: float 20s infinite;
        }

        .circle:nth-child(1) {
            width: 80px;
            height: 80px;
            left: 10%;
            animation-delay: 0s;
        }

        .circle:nth-child(2) {
            width: 120px;
            height: 120px;
            left: 30%;
            animation-delay: 2s;
        }

        .circle:nth-child(3) {
            width: 100px;
            height: 100px;
            left: 50%;
            animation-delay: 4s;
        }

        .circle:nth-child(4) {
            width: 150px;
            height: 150px;
            left: 70%;
            animation-delay: 6s;
        }

        .circle:nth-child(5) {
            width: 90px;
            height: 90px;
            left: 85%;
            animation-delay: 8s;
        }

        @keyframes float {
            0%, 100% {
                transform: translateY(100vh) scale(0);
                opacity: 0;
            }
            10% {
                opacity: 1;
            }
            90% {
                opacity: 1;
            }
            100% {
                transform: translateY(-100px) scale(1);
            }
        }

        /* Background 3: Particle Stars */
        .bg-particle-stars {
            background: linear-gradient(135deg, #0f2027 0%, #203a43 50%, #2c5364 100%);
        }

        .star {
            position: absolute;
            width: 2px;
            height: 2px;
            background: white;
            border-radius: 50%;
            animation: twinkle 3s infinite;
        }

        @keyframes twinkle {
            0%, 100% { opacity: 0; transform: scale(0); }
            50% { opacity: 1; transform: scale(1); }
        }

        /* Background 4: Mesh Gradient */
        .bg-mesh {
            background: linear-gradient(135deg, #fa709a 0%, #fee140 100%);
            position: relative;
        }

        .mesh-layer {
            position: absolute;
            width: 100%;
            height: 100%;
            background: radial-gradient(circle at 20% 50%, rgba(255, 0, 150, 0.3) 0%, transparent 50%),
                        radial-gradient(circle at 80% 80%, rgba(0, 150, 255, 0.3) 0%, transparent 50%),
                        radial-gradient(circle at 40% 20%, rgba(255, 200, 0, 0.3) 0%, transparent 50%);
            animation: meshMove 15s ease infinite;
        }

        @keyframes meshMove {
            0%, 100% { transform: translate(0, 0) scale(1); }
            33% { transform: translate(50px, 100px) scale(1.1); }
            66% { transform: translate(-50px, -50px) scale(0.9); }
        }

        /* Background 5: Wave Animation */
        .bg-waves {
            background: linear-gradient(135deg, #4facfe 0%, #00f2fe 100%);
        }

        .wave {
            position: absolute;
            bottom: 0;
            left: 0;
            width: 200%;
            height: 200px;
            background: rgba(255, 255, 255, 0.1);
            border-radius: 1000px 1000px 0 0;
            animation: wave 10s linear infinite;
        }

        .wave:nth-child(2) {
            animation-delay: -5s;
            opacity: 0.5;
            height: 180px;
        }

        .wave:nth-child(3) {
            animation-delay: -2.5s;
            opacity: 0.3;
            height: 160px;
        }

        @keyframes wave {
            0% { transform: translateX(0); }
            100% { transform: translateX(-50%); }
        }

        /* Background 6: Matrix Rain */
        .bg-matrix {
            background: #0d0d0d;
        }

        .matrix-column {
            position: absolute;
            top: -100%;
            font-family: monospace;
            font-size: 20px;
            color: #0f0;
            opacity: 0.8;
            animation: matrixFall 10s linear infinite;
        }

        @keyframes matrixFall {
            to { top: 100%; }
        }

        /* Background 7: Aurora Borealis */
        .bg-aurora {
            background: linear-gradient(135deg, #020111 0%, #3a3a52 100%);
        }

        .aurora {
            position: absolute;
            width: 100%;
            height: 100%;
            background: linear-gradient(90deg, 
                transparent 0%, 
                rgba(0, 255, 200, 0.3) 20%, 
                rgba(150, 0, 255, 0.3) 40%, 
                rgba(255, 100, 200, 0.3) 60%, 
                transparent 100%);
            animation: auroraMove 20s ease infinite;
            filter: blur(50px);
        }

        @keyframes auroraMove {
            0%, 100% { transform: translateX(-100%) translateY(0) rotate(0deg); }
            50% { transform: translateX(100%) translateY(50px) rotate(10deg); }
        }

        /* Background 8: Geometric Pattern */
        .bg-geometric {
            background: linear-gradient(135deg, #f857a6 0%, #ff5858 100%);
        }

        .geometric-shape {
            position: absolute;
            width: 200px;
            height: 200px;
            border: 2px solid rgba(255, 255, 255, 0.2);
            animation: rotate3d 20s linear infinite;
        }

        .geometric-shape:nth-child(1) {
            top: 10%;
            left: 10%;
            animation-delay: 0s;
        }

        .geometric-shape:nth-child(2) {
            top: 60%;
            right: 10%;
            animation-delay: -10s;
        }

        @keyframes rotate3d {
            0% { transform: rotate(0deg) rotateY(0deg); }
            100% { transform: rotate(360deg) rotateY(360deg); }
        }

        /* Navigation */
        .nav {
            position: fixed;
            right: 30px;
            top: 50%;
            transform: translateY(-50%);
            z-index: 100;
            display: flex;
            flex-direction: column;
            gap: 15px;
        }

        .nav-dot {
            width: 12px;
            height: 12px;
            border-radius: 50%;
            background: rgba(255, 255, 255, 0.5);
            cursor: pointer;
            transition: all 0.3s ease;
        }

        .nav-dot:hover,
        .nav-dot.active {
            background: white;
            transform: scale(1.5);
        }

        @media (max-width: 768px) {
            .content h2 {
                font-size: 2rem;
            }

            .content p {
                font-size: 1rem;
            }

            .nav {
                right: 15px;
            }
        }

    // Generate stars for particle background
        const particleSection = document.querySelector('.bg-particle-stars');
        for (let i = 0; i < 100; i++) {
            const star = document.createElement('div');
            star.className = 'star';
            star.style.left = Math.random() * 100 + '%';
            star.style.top = Math.random() * 100 + '%';
            star.style.animationDelay = Math.random() * 3 + 's';
            particleSection.appendChild(star);
        }

        // Generate matrix rain
        const matrixSection = document.querySelector('.bg-matrix');
        const chars = '01アイウエオカキクケコサシスセソタチツテト';
        for (let i = 0; i < 50; i++) {
            const column = document.createElement('div');
            column.className = 'matrix-column';
            column.style.left = Math.random() * 100 + '%';
            column.style.animationDelay = Math.random() * 10 + 's';
            column.style.animationDuration = (Math.random() * 10 + 10) + 's';
            
            let text = '';
            for (let j = 0; j < 20; j++) {
                text += chars[Math.floor(Math.random() * chars.length)] + '<br>';
            }
            column.innerHTML = text;
            matrixSection.appendChild(column);
        }

        // Navigation dots
        const sections = document.querySelectorAll('.section');
        const navDots = document.querySelectorAll('.nav-dot');

        const observer = new IntersectionObserver((entries) => {
            entries.forEach(entry => {
                if (entry.isIntersecting) {
                    const index = Array.from(sections).indexOf(entry.target);
                    navDots.forEach(dot => dot.classList.remove('active'));
                    navDots[index].classList.add('active');
                }
            });
        }, { threshold: 0.5 });

        sections.forEach(section => observer.observe(section));

        navDots.forEach(dot => {
            dot.addEventListener('click', () => {
                const sectionIndex = parseInt(dot.dataset.section);
                sections[sectionIndex].scrollIntoView({ behavior: 'smooth' });
            });
        });