What am I missing? Flexbox doesn't center the container in this snippet here

I'm trying to center the container and I don't know why it doesnt work.

html, body {
   height:100%}
.container{
   min-height:20em;
   width: fit-content; 
   background-color:#ffffff;
   display:flex;
   flex-direction:row; 
   align-items:center;
   justify-content:center; 
}````