::之前，CSS伪元素可以很容易地做到这一点!

.element { 位置:相对; 宽度:200 px; 身高:150 px; 背景图像:线性梯度(45度，蓝色，水); z - index: 2; ｝ {前.element:: 位置:绝对的; 内容:“”; 插图:0;/*与{top: 0相同;右:0;底部:0;左:0;}* / 背景-图像:线性梯度(底部，红色，橙色); z - index: 1; 透明度:0; 过渡:不透明度0.25s线性; ｝ {前.element:徘徊:: 透明度:1; ｝ 身体< > < div class = "元素" > < / div > 身体< / >

你所要做的就是使用::before不透明度为零的伪元素。

打开:悬停，切换::before的不透明度为1，如果你遵循几个简单的步骤，你应该可以让你的过渡工作。

使用background-image设置元素的背景渐变 在不透明度为0的伪元素之前使用::来设置下一个渐变 设置不透明度为1 inside:hover::before 确保你的::before有: 绝对位置 内容:“ 比默认元素更低的z-index 顶部，底部，左侧和右侧为零(或简单地插入:0) 过渡目标不透明度与您的偏好的时间间隔

就是这样!现在你应该可以用你喜欢的任何持续时间/延迟/计时函数来调整你的过渡!

一个更简洁的解决方案是设置背景色并使用蒙版图像。

#container div a {
  background-color: blue;
  transition: background 0.2s linear;
  width: 200px;
  height: 150px;
  mask-image: radial-gradient(circle at 50% 50%, rgba(0, 0, 0, .7), rgba(0, 0, 0, .4));
}

#container div a:hover { 
  background-color: red;
}

2021年:现在可以动画渐变了(Firefox和Safari还不行)

随着Chrome 85, Edge和Opera添加了对@property规则的支持，现在我们可以在CSS中这样做:

@property --myColor1 {
  syntax: '<color>';
  initial-value: magenta;
  inherits: false;
}

@property --myColor2 {
  syntax: '<color>';
  initial-value: green;
  inherits: false;
}

其余都是常规的CSS。 设置变量为初始渐变颜色，并设置这些变量的过渡:

div {
  /* Optional: change initial value of the variables */
  /* --myColor1: #f64; --myColor2: brown; */

  background: linear-gradient(var(--myColor1), var(--myColor2));
  transition: --myColor1 3s, --myColor2 3s;
}

然后，在所需的规则上，为变量设置新的值:

div:hover {  
  --myColor1: #f00;
  --myColor2: yellow;
}

@property——myColor1 { 语法:“< >颜色”; 初值:# 0 f0; 继承:错误; ｝ @property——myColor2 { 语法:“< >颜色”; 初始值:rgb(40,190,145); 继承:错误; ｝ div { 宽度:200 px; 身高:100 px; background: linear-gradient(var(——myColor1)， var(——myColor2)); ——myColor1 3s，——myColor2 3s; ｝ div:{徘徊 ——myColor1:红色; ——myColor2: # E1AF2F; ｝ <div>悬停在我上方</div>

在这里查看完整的描述和示例，并参考这里的@property规范。 @property规则是CSS Houdini技术的一部分。要了解更多信息，请参考这里和这里，并观看这个视频。

我知道这是一个老问题，但也许有人喜欢我在纯CSS解决方案的方式。从左到右渐变。

.contener{ width:300px; height:200px; background-size:cover; border:solid 2px black; } .ed { width: 0px; height: 200px; background:linear-gradient(to right, rgba(0,0,255,0.75), rgba(255,0,0,0.75)); position: relative; opacity:0; transition:width 20s, opacity 0.6s; } .contener:hover .ed{ width: 300px; background:linear-gradient(to right, rgba(0,0,255,0.75), rgba(255,0,0,0.75)); position: relative; opacity:1; transition:width 0.4s, opacity 1.1s; transition-delay: width 2s; animation-name: gradient-fade; animation-duration: 1.1s; -webkit-animation-name: gradient-fade; /* Chrome, Safari, Opera */ -webkit-animation-duration: 1.1s; /* Chrome, Safari, Opera */ } /* ANIMATION */ @-webkit-keyframes gradient-fade { 0% {background:linear-gradient(to right, rgba(0,0,255,0), rgba(255,0,0,0));} 2% {background:linear-gradient(to right, rgba(0,0,255,0.01875), rgba(255,0,0,0));} 4% {background:linear-gradient(to right, rgba(0,0,255,0.0375), rgba(255,0,0,0.0));} 6% {background:linear-gradient(to right, rgba(0,0,255,0.05625), rgba(255,0,0,0.0));} 8% {background:linear-gradient(to right, rgba(0,0,255,0.075), rgba(255,0,0,0));} 10% {background:linear-gradient(to right, rgba(0,0,255,0.09375), rgba(255,0,0,0));} 12% {background:linear-gradient(to right, rgba(0,0,255,0.1125), rgba(255,0,0,0));} 14% {background:linear-gradient(to right, rgba(0,0,255,0.13125), rgba(255,0,0,0));} 16% {background:linear-gradient(to right, rgba(0,0,255,0.15), rgba(255,0,0,0));} 18% {background:linear-gradient(to right, rgba(0,0,255,0.16875), rgba(255,0,0,0));} 20% {background:linear-gradient(to right, rgba(0,0,255,0.1875), rgba(255,0,0,0));} 22% {background:linear-gradient(to right, rgba(0,0,255,0.20625), rgba(255,0,0,0.01875));} 24% {background:linear-gradient(to right, rgba(0,0,255,0.225), rgba(255,0,0,0.0375));} 26% {background:linear-gradient(to right, rgba(0,0,255,0.24375), rgba(255,0,0,0.05625));} 28% {background:linear-gradient(to right, rgba(0,0,255,0.2625), rgba(255,0,0,0.075));} 30% {background:linear-gradient(to right, rgba(0,0,255,0.28125), rgba(255,0,0,0.09375));} 32% {background:linear-gradient(to right, rgba(0,0,255,0.3), rgba(255,0,0,0.1125));} 34% {background:linear-gradient(to right, rgba(0,0,255,0.31875), rgba(255,0,0,0.13125));} 36% {background:linear-gradient(to right, rgba(0,0,255,0.3375), rgba(255,0,0,0.15));} 38% {background:linear-gradient(to right, rgba(0,0,255,0.35625), rgba(255,0,0,0.16875));} 40% {background:linear-gradient(to right, rgba(0,0,255,0.375), rgba(255,0,0,0.1875));} 42% {background:linear-gradient(to right, rgba(0,0,255,0.39375), rgba(255,0,0,0.20625));} 44% {background:linear-gradient(to right, rgba(0,0,255,0.4125), rgba(255,0,0,0.225));} 46% {background:linear-gradient(to right, rgba(0,0,255,0.43125),rgba(255,0,0,0.24375));} 48% {background:linear-gradient(to right, rgba(0,0,255,0.45), rgba(255,0,0,0.2625));} 50% {background:linear-gradient(to right, rgba(0,0,255,0.46875), rgba(255,0,0,0.28125));} 52% {background:linear-gradient(to right, rgba(0,0,255,0.4875), rgba(255,0,0,0.3));} 54% {background:linear-gradient(to right, rgba(0,0,255,0.50625), rgba(255,0,0,0.31875));} 56% {background:linear-gradient(to right, rgba(0,0,255,0.525), rgba(255,0,0,0.3375));} 58% {background:linear-gradient(to right, rgba(0,0,255,0.54375), rgba(255,0,0,0.35625));} 60% {background:linear-gradient(to right, rgba(0,0,255,0.5625), rgba(255,0,0,0.375));} 62% {background:linear-gradient(to right, rgba(0,0,255,0.58125), rgba(255,0,0,0.39375));} 64% {background:linear-gradient(to right,rgba(0,0,255,0.6), rgba(255,0,0,0.4125));} 66% {background:linear-gradient(to right, rgba(0,0,255,0.61875), rgba(255,0,0,0.43125));} 68% {background:linear-gradient(to right, rgba(0,0,255,0.6375), rgba(255,0,0,0.45));} 70% {background:linear-gradient(to right, rgba(0,0,255,0.65625), rgba(255,0,0,0.46875));} 72% {background:linear-gradient(to right, rgba(0,0,255,0.675), rgba(255,0,0,0.4875));} 74% {background:linear-gradient(to right, rgba(0,0,255,0.69375), rgba(255,0,0,0.50625));} 76% {background:linear-gradient(to right, rgba(0,0,255,0.7125), rgba(255,0,0,0.525));} 78% {background:linear-gradient(to right, rgba(0,0,255,0.73125),,rgba(255,0,0,0.54375));} 80% {background:linear-gradient(to right, rgba(0,0,255,0.75), rgba(255,0,0,0.5625));} 82% {background:linear-gradient(to right, rgba(0,0,255,0.75), rgba(255,0,0,0.58125));} 84% {background:linear-gradient(to right, rgba(0,0,255,0.75),rgba(255,0,0,0.6));} 86% {background:linear-gradient(to right, rgba(0,0,255,0.75), rgba(255,0,0,0.61875));} 88% {background:linear-gradient(to right, rgba(0,0,255,0.75), rgba(255,0,0,0.6375));} 90% {background:linear-gradient(to right, rgba(0,0,255,0.75), rgba(255,0,0,0.65625));} 92% {background:linear-gradient(to right, rgba(0,0,255,0.75), rgba(255,0,0,0.675));} 94% {background:linear-gradient(to right, rgba(0,0,255,0.75),rgba(255,0,0,0.69375));} 96% {background:linear-gradient(to right, rgba(0,0,255,0.75), rgba(255,0,0,0.7125));} 98% {background:linear-gradient(to right, rgba(0,0,255,0.75), rgba(255,0,0,0.73125),);} 100% {background:linear-gradient(to right, rgba(0,0,255,0.75), rgba(255,0,0,0.75));} } <div class="contener" style=""> <div class="ed"></div> </div>

渐变过渡的部分解决方法是使用嵌入框阴影——你可以转换框阴影本身，也可以转换背景颜色——例如，如果你创建的嵌入框阴影与背景颜色相同，然后在背景颜色上使用过渡，它会产生一种错觉，即普通背景正在变为径向渐变

.button SPAN {
    padding: 10px 30px; 
    border: 1px solid ##009CC5;

    -moz-box-shadow: inset 0 0 20px 1px #00a7d1;
    -webkit-box-shadow: inset 0 0 20px 1px#00a7d1;
    box-shadow: inset 0 0 20px 1px #00a7d1; 

    background-color: #00a7d1;
    -webkit-transition: background-color 0.5s linear;
    -moz-transition: background-color 0.5s linear;
    -o-transition: background-color 0.5s linear;
    transition: background-color 0.5s linear;
}

.button SPAN:hover {
    background-color: #00c5f7; 
}

你可以伪造渐变之间的过渡，在一些堆叠渐变的不透明度中使用过渡，正如这里的一些答案所描述的:

CSS3动画与梯度。

你也可以转换位置，如下所述:

CSS3渐变过渡与背景位置。

这里还有一些技巧:

动画CSS3渐变。