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CSS 动画

· 6 min

CSS 动画通过 @keyframes 定义动画序列，使用 animation 属性控制播放。与过渡不同，动画可以自动播放、循环、暂停，适合更复杂的视觉效果。

@keyframes 定义动画#

基本语法#

@keyframes slide-in {
  from {
    transform: translateX(-100%);
    opacity: 0;
  }
  to {
    transform: translateX(0);
    opacity: 1;
  }
}

百分比关键帧#

@keyframes bounce {
  0% {
    transform: translateY(0);
  }
  25% {
    transform: translateY(-20px);
  }
  50% {
    transform: translateY(0);
  }
  75% {
    transform: translateY(-10px);
  }
  100% {
    transform: translateY(0);
  }
}

多个属性#

@keyframes fade-scale {
  0% {
    opacity: 0;
    transform: scale(0.8);
  }
  50% {
    opacity: 1;
  }
  100% {
    opacity: 1;
    transform: scale(1);
  }
}

animation 属性#

简写语法#

.element {
  animation: name duration timing-function delay iteration-count direction
    fill-mode play-state;
}


/* 示例 */
.box {
  animation: slide-in 0.5s ease-out 0.2s 1 normal forwards running;
}

单独属性#

.box {
  animation-name: slide-in;
  animation-duration: 0.5s;
  animation-timing-function: ease-out;
  animation-delay: 0.2s;
  animation-iteration-count: 1;
  animation-direction: normal;
  animation-fill-mode: forwards;
  animation-play-state: running;
}

animation-duration#

动画持续时间：

.fast {
  animation-duration: 0.3s;
}
.normal {
  animation-duration: 1s;
}
.slow {
  animation-duration: 3s;
}

animation-timing-function#

速度曲线（同 transition）：

.ease {
  animation-timing-function: ease;
}
.linear {
  animation-timing-function: linear;
}
.bounce {
  animation-timing-function: cubic-bezier(0.68, -0.55, 0.265, 1.55);
}

逐帧动画#

.sprite {
  animation-timing-function: steps(8);
}

animation-iteration-count#

播放次数：

.once {
  animation-iteration-count: 1;
}
.twice {
  animation-iteration-count: 2;
}
.infinite {
  animation-iteration-count: infinite;
}

animation-direction#

播放方向：

.normal {
  animation-direction: normal;
} /* 正向 */
.reverse {
  animation-direction: reverse;
} /* 反向 */
.alternate {
  animation-direction: alternate;
} /* 正向 → 反向交替 */
.alternate-reverse {
  animation-direction: alternate-reverse;
} /* 反向 → 正向交替 */

animation-fill-mode#

动画前后的样式：

.none {
  animation-fill-mode: none;
} /* 默认：动画前后恢复原样 */
.forwards {
  animation-fill-mode: forwards;
} /* 保持最后一帧 */
.backwards {
  animation-fill-mode: backwards;
} /* 延迟期间应用第一帧 */
.both {
  animation-fill-mode: both;
} /* 结合 forwards 和 backwards */

animation-play-state#

控制播放/暂停：

.running {
  animation-play-state: running;
}
.paused {
  animation-play-state: paused;
}


/* 悬停暂停 */
.animated:hover {
  animation-play-state: paused;
}

多动画#

.element {
  animation:
    slide-in 0.5s ease forwards,
    fade-in 0.3s ease,
    pulse 2s infinite 1s;
}

实战案例#

加载动画#

/* 旋转加载器 */
@keyframes spin {
  from {
    transform: rotate(0deg);
  }
  to {
    transform: rotate(360deg);
  }
}


.spinner {
  width: 40px;
  height: 40px;
  border: 3px solid #e5e7eb;
  border-top-color: #3b82f6;
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}


/* 脉冲效果 */
@keyframes pulse {
  0%,
  100% {
    opacity: 1;
  }
  50% {
    opacity: 0.5;
  }
}


.skeleton {
  background: #e5e7eb;
  animation: pulse 1.5s ease-in-out infinite;
}


/* 弹跳点 */
@keyframes bounce-dots {
  0%,
  80%,
  100% {
    transform: translateY(0);
  }
  40% {
    transform: translateY(-10px);
  }
}


.loading-dots span {
  display: inline-block;
  width: 8px;
  height: 8px;
  background: #3b82f6;
  border-radius: 50%;
  animation: bounce-dots 1.4s ease-in-out infinite;
}


.loading-dots span:nth-child(2) {
  animation-delay: 0.2s;
}


.loading-dots span:nth-child(3) {
  animation-delay: 0.4s;
}

入场动画#

@keyframes fade-up {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}


.animate-fade-up {
  animation: fade-up 0.5s ease forwards;
}


/* 交错入场 */
.stagger > * {
  opacity: 0;
  animation: fade-up 0.5s ease forwards;
}


.stagger > *:nth-child(1) {
  animation-delay: 0.1s;
}
.stagger > *:nth-child(2) {
  animation-delay: 0.2s;
}
.stagger > *:nth-child(3) {
  animation-delay: 0.3s;
}
.stagger > *:nth-child(4) {
  animation-delay: 0.4s;
}

注意力动画#

/* 摇晃 */
@keyframes shake {
  0%,
  100% {
    transform: translateX(0);
  }
  10%,
  30%,
  50%,
  70%,
  90% {
    transform: translateX(-5px);
  }
  20%,
  40%,
  60%,
  80% {
    transform: translateX(5px);
  }
}


.shake {
  animation: shake 0.5s ease;
}


/* 心跳 */
@keyframes heartbeat {
  0%,
  100% {
    transform: scale(1);
  }
  14% {
    transform: scale(1.1);
  }
  28% {
    transform: scale(1);
  }
  42% {
    transform: scale(1.1);
  }
  70% {
    transform: scale(1);
  }
}


.heartbeat {
  animation: heartbeat 1.5s ease-in-out infinite;
}


/* 闪烁 */
@keyframes blink {
  0%,
  100% {
    opacity: 1;
  }
  50% {
    opacity: 0;
  }
}


.blink {
  animation: blink 1s step-end infinite;
}

悬浮效果#

@keyframes float {
  0%,
  100% {
    transform: translateY(0);
  }
  50% {
    transform: translateY(-10px);
  }
}


.float {
  animation: float 3s ease-in-out infinite;
}


/* 光晕效果 */
@keyframes glow {
  0%,
  100% {
    box-shadow: 0 0 5px rgba(59, 130, 246, 0.5);
  }
  50% {
    box-shadow: 0 0 20px rgba(59, 130, 246, 0.8);
  }
}


.glow {
  animation: glow 2s ease-in-out infinite;
}

进度指示#

@keyframes progress {
  from {
    width: 0;
  }
  to {
    width: 100%;
  }
}


.progress-bar {
  height: 4px;
  background: #3b82f6;
  animation: progress 2s ease forwards;
}


/* 不确定进度 */
@keyframes indeterminate {
  0% {
    transform: translateX(-100%);
  }
  100% {
    transform: translateX(400%);
  }
}


.progress-indeterminate {
  width: 25%;
  height: 4px;
  background: #3b82f6;
  animation: indeterminate 1.5s ease-in-out infinite;
}

打字机效果#

@keyframes typing {
  from {
    width: 0;
  }
  to {
    width: 100%;
  }
}


@keyframes cursor {
  0%,
  100% {
    border-color: transparent;
  }
  50% {
    border-color: currentColor;
  }
}


.typewriter {
  overflow: hidden;
  white-space: nowrap;
  border-right: 2px solid;
  animation:
    typing 3s steps(30) forwards,
    cursor 0.75s step-end infinite;
}

动画事件#

JavaScript 可以监听动画事件：

element.addEventListener('animationstart', handleStart)
element.addEventListener('animationend', handleEnd)
element.addEventListener('animationiteration', handleIteration)

性能优化#

使用 transform 和 opacity#

/* 好：只改变 transform 和 opacity */
@keyframes good {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}


/* 避免：改变布局属性 */
@keyframes avoid {
  from {
    height: 0;
  }
  to {
    height: 100px;
  }
}

GPU 加速#

.gpu-accelerated {
  transform: translateZ(0);
  /* 或 */
  will-change: transform, opacity;
}

减少动画#

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}

常见问题#

🤔 动画结束后元素消失？

使用 animation-fill-mode: forwards 保持最后一帧状态。

🤔 动画闪烁？

添加 backface-visibility: hidden 或 transform: translateZ(0)。

🤔 如何重新触发动画？

element.classList.remove('animate')
void element.offsetWidth // 触发重排
element.classList.add('animate')

CSS 动画为网页带来生命力。合理使用动画可以引导用户注意力、提供反馈、增加趣味性。下一篇我们将学习 CSS 变换和滤镜，它们是实现视觉效果的强大工具。