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CSS - Play animation while hovering, but not with an abrupt end

I am trying to create a sort of loading animation, with 3 bars that are below eachother that all have seperate keyframes.
The 3 bars are div elements, located inside a parent div.
<div id="menu">
<div id="menubox1"></div>
<div id="menubox2"></div>
<div id="menubox3"></div>
</div>
The animation properties are assigned to the individual menubox ids.
#menubox1:after {
content: '';
position: absolute;
bottom: 0px;
transform: translateY(-50%);
border-top: 1px solid #FFDADA;
animation: menukeyframes1;
animation-duration: 2000ms;
animation-iteration-count: infinite;
animation-timing-function: ease-in-out;
animation-play-state: inherit;
}
#keyframes menukeyframes1 {
0% { width: 100%; left:0;}
...
}
My goal is to play the animation while the cursor is hovering over the parent div.
My attempt was to play around with animation-play-state which was set to running or paused, depending if the parent div was hovered.
The problem is that the animation is immediatly paused, before the animation is complete, which looks kind of bad if it stops mid-motion.
Is there a good fix for this, preferrably without JavaScript/jQuery, and across all browsers?

As you see it can't be done with just CSS at this moment, and as good jquery answers are already referenced, it's worth to mention that it could be solved in few lines of vanillaJS:
var dur = 2000;
document.querySelectorAll('.smooth').forEach(el=>{
var t;
el.addEventListener('mouseover',_=>{t = performance.now();el.style.animationPlayState = 'running'})
el.addEventListener('mouseout',_=>window.setTimeout(()=>el.style.animationPlayState = 'paused',dur-(performance.now()-t)%dur));
})
working pen
non-es6: BABEL

You can always fade out the animated divs using transitions.
Something like this might work for you:
#menubox1 {
opacity: 0;
transition: opacity .5s linear;
}
#menu:hover {
#menubox1 {
opacity: 1;
transition: opacity .5s linear;
}
}

CSS animation : move a div with the new position relative to the previous

for better performance, I want replace:
$('#foo').animate({ left: '+=42px' }, 500);
by a transition (or animation) CSS3.
But how can we do to implement "+=" on left property in CSS?
How move a div with the new left position relative to the previous?
thx.

In vanilla-js you can't use +=, but you can get the old value instead:
document.getElementById('foo').onclick = function() {
this.style.left = parseFloat(getComputedStyle(this).left) + 42 + 'px';
};
#foo {
position: relative;
left: 0;
transition: 2s left;
}
<div id="foo">Click me multiple times</div>

You can use the transition for smooth animation. you just put transition settings in the CSS of an element like this,
#foo {
-webkit-transition: all 0.5s ease-out;
-o-transition: all 0.5s ease-out;
-moz-transition: all 0.5s ease-out;
transition: all 0.5s ease-out
}
Then do your incrementation of left with script like this.
$('#foo').css('left', '+=42px');
You can refer to this page.

jQuery toggleClass - can't animate or give it a transition

I'm having a small issue with my code. I have an element that when the page scrolls it will appear. However, I cannot get it to "appear" in a smoother way. I have tried CSS transitions and attempted fadeIn but neither work. It always just "jumps" in, I cannot get it to ease in.
Here is the code:
$(window).on("scroll", function () {
$('.navbar').toggleClass('visible', $(document).scrollTop() > 40);
});
So it appears just fine, but I can't figure out how to animate adding the class name.
This is the CSS btw:
.navbar {
visibility: hidden;
}
.navbar.visible {
visibility: visible;
}

visibility can't be animated with CSS transitions.
But you can do :
.navbar {
opacity: 0;
transition: opacity .5s ease; // Feel free to use prefixes.
}
.navbar.visible {
opacity: 1;
}
CSS transition / animations is surely the best way to animate something in 2014. You should avoid fadeToggle() and others jQuery animation methods.

instead of using toggleClass, use fadeToggle. it will do everything for u as far as CSS..
give it a try, just fadeToggle();

Here is the example of your code with correct css transition. You cannot animate visibility, but you can play with position and opacity.
http://jsfiddle.net/xZ6fm/
.navbar {
position: fixed;
top: -100px;
left: 0; right: 0;
padding: 12px;
opacity: 0;
background: #ccc;
}
.navbar.visible {
top: 0;
opacity: 1;
-webkit-transition: top 0.3s linear, opacity 0.7s linear;
-moz-transition: top 0.3s linear, opacity 0.7s linear;
transition: top 0.3s linear, opacity 0.7s linear;
}

As indicated in the other answer, fadeToggle() will get the work done for you. And frankly, it's probably the easiest way to accomplish such an effect.
CSS transitions require the transition property. Place this block of code in each of your CSS declarations:
transition: visibility .25s linear;
-webkit-transition: visibility .25s linear;
-moz-transition: visibility .25s linear;
-o-transition: visibility .25s linear;
If you have difficulties with visibility, try using opacity instead.

Make CSS hover element permanent onclick

So I have created a little box with some CSS animation:
.boxtest
{
width: 50px;
height: 50px;
background-color: green;
opacity: .2;
transition: opacity .8s, width .8s ease-out;
-moz-transition: opacity .8s, width .8s ease-out;
-webkit-transition: opacity .8s, width .8s ease-out;
-o-transition: opacity .8s, width.8s ease-out;
}
.boxtest:hover {
opacity: 1;
width: 70%;
}
What I'd like is for the CSS hover class to remain permanent after the user has hovered their mouse over the element.
I guess you'd need to use Javascript, but I'm no expert so can't figure out the right command. Any help would be awesome!
http://jsfiddle.net/r75gC/

Here you go!
Basically I used jQuery to add a class to the div. You can choose one of the two below.
//onClick
$(".boxtest").on("click", function () {
$(".boxtest").addClass('permahover');
});
//onHover
$(".boxtest").on("mouseenter", function () {
$(".boxtest").addClass('permahover');
});
I changed the CSS to:
.boxtest:hover,
.permahover {
opacity: 1;
width: 70%;
}
http://jsfiddle.net/rFRc5/2/

If you haven't a lot of experience with javascript I would recommend using JQuery. Use this to include the JQuery libraries in your website:
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
this will allow you to simply do (in your html file):
<script>
$(".boxtest").mouseenter(function() { $(".boxtest").addClass("boxtestHover"); });
</script>
also for the above change .boxtest:hover to boxtesthover (or whatever you want)

jQuery is a bit overkill for this.
Instead of hover, use another class name, then just add this to the element
onmouseover="this.className='newClassName'"

css3 image fadein

I'm trying to have images fade in with css3 once they're loaded. The problem is the way my methods are currently chained it fades it in and out for a split second twice. instead of just being blank and fading in.
my solution was to try and split out the animation code into a seperate class that i apply AFTER i initially set the opacity to zero (i do this in JS so people without js enabled can still see the images).
It's still not working though
I assume its because in this code its setting the opacity to zero and immediately adding an animation transition class which somehow catches the opacity .css() method while its changing still (dont know how this is possible,... shouldnt it complete opacity before moving on to add class?)
// nice thumbnail loading
$('.thumb').css('opacity','0').addClass('thumb-animated').on('load', function(){
$(this).css('opacity','1');
});
.resources .thumb-animated {
-webkit-transition: opacity .2s;
-moz-transition: opacity .2s;
-ms-transition: opacity .2s;
-o-transition: opacity .2s;
transition: opacity .2s;
}

Well...
Why do you set opacity to 1 in jQuery?
If you want to use CSS3 and not simply fadeIn(200) why don't you add "opacity: 1" to css class thumb-animated?
EDIT:
Note that load will not be triggered if the image is already in cache.
Also, !important has to be added to rewrite the rule modified via javascript.
There you go: http://jsfiddle.net/enTCe/5/
This seems to work perfectly outside JSfiddle, on JSfiddle looks like it waits for all the images to be loaded.

What about using just css animations? No JS code is needed.
#-webkit-keyframes opacityChange {
0% { opacity: 0; }
100% { opacity: 1; }
}
#-moz-keyframes opacityChange {
0% { opacity: 0; }
100% { opacity: 1; }
}
#-ms-keyframes opacityChange {
0% { opacity: 0; }
100% { opacity: 1; }
}
.thumb {
width: 200px;
height: 200px;
opacity: 1;
-webkit-animation: opacityChange 5s;
-moz-animation: opacityChange 5s;
-ms-animation: opacityChange 5s;
}

You can wait adding the class to the image is loaded
$('.thumb').css('opacity','0').on('load', function(){
$(this).addClass('thumb-animated').css('opacity','1');
});

Try something like this:
$('#thumb').hide();
myImg = $('<img>').attr('src', 'thumb.png').load(function(){
$('#thumb').html(myImg).fadeIn(200);
});