随机渐变背景

 <style>
        html,
        body {
            margin: 0;
        }
        body:after {
            content: 'click to update';
            font-size: 0.8em;
            color: rgba(0, 0, 0, 0.3);
            position: fixed;
            width: 100%;
            bottom: 1em;
            text-align: center;
        }

        #cloud {
            overflow: hidden;
            width: 1px;
            height: 1px;
            transform: translate(-100%, -100%);
            border-radius: 50%;
            filter: url(#filter);
        }
    </style>
    <body>
        <div id="cloud"></div>

        <svg width="0">
            <filter id="filter">
                <feTurbulence
                    type="fractalNoise"
                    baseFrequency=".01"
                    numOctaves="10"
                />
                <feDisplacementMap in="SourceGraphic" scale="240" />
            </filter>
        </svg>
    </body>

    <script>
        function rn(from, to) {
            return ~~(Math.random() * (to - from + 1)) + from
        }

        function rs() {
            return arguments[rn(1, arguments.length) - 1]
        }

        function boxShadows(max) {
            let ret = []
            for (let i = 0; i < max; ++i) {
                ret.push(`
      ${rn(1, 100)}vw ${rn(1, 100)}vh ${rn(20, 40)}vmin ${rn(1, 20)}vmin
      ${rs('#11cbd7', '#c6f1e7', '#f0fff3', '#fa4659')}
    `)
            }
            return ret.join(',')
        }

        const cloud = document.querySelector('#cloud')
        function update() {
            cloud.style.boxShadow = boxShadows(100)
        }

        window.addEventListener('load', update)
        document.addEventListener('click', update)
    </script>
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随机渐变背景
