CSS how to make an element fade in and then fade o

问题:

I can make an element with an opacity of zero fade in by changing its class to .elementToFadeInAndOut with the following css:

.elementToFadeInAndOut {
    opacity: 1;
    transition: opacity 2s linear;
}

Is there a way I can make the element fade out after it fades in by editing css for this same class?

Thank you very much for your time.

回答1:

Use css @keyframes

.elementToFadeInAndOut {
    opacity: 1;
    animation: fade 2s linear;
}


@keyframes fade {
  0%,100% { opacity: 0 }
  50% { opacity: 1 }
}

here is a DEMO

.elementToFadeInAndOut {
    width:200px;
    height: 200px;
    background: red;
    -webkit-animation: fadeinout 4s linear forwards;
    animation: fadeinout 4s linear forwards;
}

@-webkit-keyframes fadeinout {
  0%,100% { opacity: 0; }
  50% { opacity: 1; }
}

@keyframes fadeinout {
  0%,100% { opacity: 0; }
  50% { opacity: 1; }
}

<div class=elementToFadeInAndOut></div>

Reading: Using CSS animations

You can clean the code by doing this:

.elementToFadeInAndOut {
    width:200px;
    height: 200px;
    background: red;
    -webkit-animation: fadeinout 4s linear forwards;
    animation: fadeinout 4s linear forwards;
    opacity: 0;
}

@-webkit-keyframes fadeinout {
  50% { opacity: 1; }
}

@keyframes fadeinout {
  50% { opacity: 1; }
}

<div class=elementToFadeInAndOut></div>

回答2:

If you need a single fadeIn/Out without an explicit user action (like a mouseover/mouseout) you may use a CSS3 animation: http://codepen.io/anon/pen/bdEpwW

.elementToFadeInAndOut {
    -webkit-animation: fadeinout 4s linear 1 forwards;
    animation: fadeinout 4s linear 1 forwards;
}

@-webkit-keyframes fadeinout {
  0% { opacity: 0; }
  50% { opacity: 1; }
  100% { opacity: 0; }
}

@keyframes fadeinout {
  0% { opacity: 0; }
  50% { opacity: 1; }
  100% { opacity: 0; }
}

By setting animation-fill-mode: forwards the animation will retain its last keyframe

By setting animation-iteration-count: 1 the animation will run just once (change this value if you need to repeat the effect more than once)

回答3:

Try this:

@keyframes animationName {
  0%   { opacity:0; }
  50%  { opacity:1; }
  100% { opacity:0; }
}
@-o-keyframes animationName{
  0%   { opacity:0; }
  50%  { opacity:1; }
  100% { opacity:0; }
}
@-moz-keyframes animationName{
  0%   { opacity:0; }
  50%  { opacity:1; }
  100% { opacity:0; }
}
@-webkit-keyframes animationName{
  0%   { opacity:0; }
  50%  { opacity:1; }
  100% { opacity:0; }
}   
.elementToFadeInAndOut {
   -webkit-animation: animationName 5s infinite;
   -moz-animation: animationName 5s infinite;
   -o-animation: animationName 5s infinite;
    animation: animationName 5s infinite;
}