Grow :before content width from center - css

Question

I've recently discovered the following approach for text-progress styling and wonder if there is a workaround to grow the element width from the center, so the text would also fill the from center instead of from the left side.
body {
background-color: black;
}
p {
color: rgba(255, 255, 255, .4);
font-family: Arial, Helvetica, sans-serif;
font-size: 40px;
height: 85px;
position: relative;
}
p:before {
max-width: 100%;
width: 0;
height: 85px;
color: #fff;
position: absolute;
top: 0;
left: 0;
overflow: hidden;
content: attr(data-text);
display: block;
animation: background-fill 15s ease-in-out infinite forwards;
}
#keyframes background-fill {
0% {
width: 0;
}
100% {
width: 100%;
}
}
<p data-text='Text'>Text</p>

Answer 1

You can achieve that by also animate left and text-indent
I also changed your p to display as inline-block, so it animate the text and not white space.
Thanks to Gaby aka G. Petrioli, it appears Firefox have issue with percent-based text-indent, so I added a CSS hack to overcome that. And again thanks to Gaby, for his now delete answer, that solved the Firefox issue (though unfortunately fails on IE)
body {
background-color: black;
}
p {
color: rgba(255, 255, 255, .4);
font-family: Arial, Helvetica, sans-serif;
font-size: 40px;
height: 85px;
position: relative;
display: inline-block;
}
p:before {
max-width: 100%;
width: 0;
height: 85px;
color: #fff;
position: absolute;
top: 0;
left: 0;
overflow: hidden;
content: attr(data-text);
display: block;
animation: background-fill 5s ease-in-out infinite forwards;
}
#keyframes background-fill {
0% {
left: 50%;
text-indent: -50%;
width: 0;
}
100% {
left: 0;
text-indent: 0;
width: 100%;
}
}
/* Begin - Firefox bug fix */
#supports (-moz-appearance:meterbar) and (display:flex) {
p:before {
width: auto;
right: 50%;
left: 50%;
display: flex;
justify-content: center;
}
#keyframes background-fill {
0% {
right: 50%;
left: 50%;
}
100% {
right: 0;
left: 0;
}
}
}
/* End - Firefox bug fix */
<p data-text='Text'>Text</p>
An alternative to the CSS hack, is a small script, that, on page load, measure the actual width of the element and set the text-indent as px instead of %.