[css] CSS how to make an element fade in and then fade out?

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?

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;
}

I found this link to be useful: css-tricks fade-in fade-out css.

Here's a summary of the csstricks post:

CSS classes:

.m-fadeOut {
  visibility: hidden;
  opacity: 0;
  transition: visibility 0s linear 300ms, opacity 300ms;
}
.m-fadeIn {
  visibility: visible;
  opacity: 1;
  transition: visibility 0s linear 0s, opacity 300ms;
}

In React:

toggle(){
    if(true condition){
        this.setState({toggleClass: "m-fadeIn"});
    }else{
        this.setState({toggleClass: "m-fadeOut"});
    }
}

render(){
    return (<div className={this.state.toggleClass}>Element to be toggled</div>)
}

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 {

    animation: fadeinout 4s linear 1 forwards;
}



@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)

A way to do this would be to set the color of the element to black, and then fade to the color of the background like this:

<style> 
p {
animation-name: example;
animation-duration: 2s;
}

@keyframes example {
from {color:black;}
to {color:white;}
}
</style>
<p>I am FADING!</p>

I hope this is what you needed!