Some screen kisses in film history.
"Gone with the Wind", again crosslit, him in red, her in white:
"Cabaret" -- there's a crosslight here, meaning that Michael York is edge lit by a tiny lamp on the floor:
You see the shadowing as people get closer:
"Blade Runner" -- Harrison Ford isn't even lit, just silhouetted by some background area that is lit:
Of course, most of these examples are profile 2-shots, i.e. 50/50's, which works not just because it's the only way to see the lips during a kiss, but it gives equal dramatic weight to both characters, creating a connection. You can shoot kissing in over-the-shoulders too, it's just that at some point, the person leaning in will block the face of the person they are kissing. In this shot, it works because he's kissing the side of her face so we can still see her expression: