@AlonGvili and @psDevUK - Thank you for the suggestions!
I managed to get it working by modifying the UDTheme like you suggested and using the CSS code from v1.7.0. I was using the stock Azure theme, but using this instead makes it look like it used to:
$theme = New-UDTheme -name 'MyTheme' -Definition @{
".card-content svg" = @{
'font-size'= '4em'
'opacity' = '.05'
'float' = 'left'
'position' = 'absolute'
'top' = '20px'
'margin-left' = '70px'
}
} -Parent 'Azure'