How to center svg as background? - html

Question

I have an SVG image (svg tag with path) and I want to make it into a whole-page fixed background. I managed to do that, but unfortunately, it's attached to the left and top side of the page, it's not centered when in mobile, etc.
Is it possible to center it horizontally and vertically?
.gradbg{
min-width:100%;
height:100%;
position:fixed;
top:0;
z-index:-1;
display:flex;
align-items:center;
justify-content:center;
}
.gradString{
object-fit:cover;
width:100%;
height:100%;
}
.gradPath{
fill:url(#Gradient1);
}
<div class="gradbg">
<svg xmlns="http://www.w3.org/2000/svg" class="gradString">
<defs> <linearGradient id="Gradient1">
<stop class="ucpgrad1bg" offset="0%"/>
<stop class="ucpgrad2bg" offset="25%"/>
<stop class="ucpgrad3bg" offset="50%"/>
<stop class="ucpgrad4bg" offset="75%"/>
<stop class="ucpgrad5bg" offset="100%"/>
</linearGradient></defs>
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