CSS transition background color without a hover - css

Question

I have a div called time-box. Sometimes I will also include an additional class called countdown. If countdown is added then I would like to use a CSS transition effect so the background changes to be red over the course of 60 seconds. In other words, each second that passes the red background gets a little wider until eventually all of the green background has gone.
I have found similar posts here but they all seem to relate to hover
Here is a fiddle
https://jsfiddle.net/e2vbheew/

Answer 1

I don't know a "simple" way to get what you want going from left to right, but there's a way you can create it using before and after pseudoelements. The key here is I'm going to create a :before pseudoelement that has the new background that transitions across, and an :after pseudoelement that replicates the content and puts it on top of the before, so it's still visible. This required putting the content in an attribute on the div so I could reference it in the 'content' of the pseudoelement. If you had more complex content inside, you could probably do away with the :after and simply give the internal content position and z-index to make sure it's visible. Here's the resulting CSS
.time-box {
height: 27px;
text-align: center;
background-color: #25E57B;
font-size:2rem;
padding:0px;
font-size:1.2rem;
text-transform:uppercase;
padding:3px 5px 3px 5px;;
font-weight:600;
height:auto;
position: relative;
}
.time-box:before {
background-color: red;
position: absolute;
left:0;
top: 0;
height: 100%;
width: 0;
content: " ";
transition: width 60s ease;
}
.countdown:after {
content: attr(data-content);
width: 100%;
text-align: center;
height: 100%;
position: absolute;
left: 0;
top: center;
z-index: 1;
}
.countdown:before {
width:100%;
}
And updated fiddle: https://jsfiddle.net/tunzwqd7/2/

Answer 2

Using CSS animation property...
.time-box {
height: 27px;
text-align: center;
background-color: #25E57B;
font-size: 2rem;
padding: 0px;
font-size: 1.2rem;
text-transform: uppercase;
padding: 3px 5px 3px 5px;
font-weight: 600;
height: auto;
position: relative;
z-index: 1;
}
.time-box.countdown:before {
content: '';
width: 0;
height: 100%;
display: block;
position: absolute;
top: 0;
left: 0;
background: red;
animation: countdown 60s forwards;
z-index: -1;
}
#keyframes countdown {
0% {
width: 0;
}
100% {
width: 100%;
}
}
<div class="time-box">
12:00
</div>
<div class="time-box countdown">
<span>12:00</span>
</div>

Answer 3

You would need to add a maximum and a little more math to make the 100% divisible by 60, but this should get you on the right track. Currently this code updates every second and adds 1% to the progress bar width with each iteration.
var time = 0;
var bar = document.querySelector('.countdown .progress-bar');
window.setInterval(function(){
time++;
bar.style.width = time+"%";
}, 1000);
.time-box {
height: 27px;
text-align: center;
background-color: #25E57B;
font-size:2rem;
padding:0px;
font-size:1.2rem;
text-transform:uppercase;
padding:3px 5px 3px 5px;;
font-weight:600;
height:auto;
position: relative;
}
.progress-bar {
display: none;
}
.countdown .progress-bar {
display: block;
position: absolute;
left: 0;
top: 0;
bottom: 0;
background: red;
width: 0%;
z-index: 1;
transition: all 0.3s ease-out;
}
.countdown p {
z-index: 2;
position: relative;
}
<div class="time-box">
<p>12:00</p>
<div class="progress-bar"></div>
</div>
<div class="time-box countdown">
<p>12:00</p>
<div class="progress-bar"></div>
</div>