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<meta charset="UTF-8">
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<title>Document</title>
<style>
h1 span {
background: linear-gradient(to right, #ec695c, #61c454) no-repeat right bottom;
background-size: 0 2px;
transition: background-size 1300ms;
}
h1 span:hover {
background-position-x: left;
background-size: 100% 2px;
}
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</head>
<body>
<h1>
<span>爱你一万年，爱你永不会改变</span>
</h1>
</body>
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