#a { background-image: radial-gradient(red, blue); }
#b { background-image: radial-gradient(red, blue); }
#c { background-image: radial-gradient(red, blue); }
#d { background-image: radial-gradient(red, blue); }
#e { background-image: radial-gradient(at calc(50%) calc(50%), red, blue); }
#f { background-image: radial-gradient(at calc(50% * sign(1em - 1px)) calc(50% * sign(1em - 1px)), red, blue); }
Computed:
#a: radial-gradient(rgb(255, 0, 0), rgb(0, 0, 255))
#b: radial-gradient(rgb(255, 0, 0), rgb(0, 0, 255))
#c: radial-gradient(rgb(255, 0, 0), rgb(0, 0, 255))
#d: radial-gradient(rgb(255, 0, 0), rgb(0, 0, 255))
#e: radial-gradient(rgb(255, 0, 0), rgb(0, 0, 255))
#f: radial-gradient(rgb(255, 0, 0), rgb(0, 0, 255))