A design tips for styling the Blogger embedded comment form for dark theme.
Take Blogger's default themes for example: Contempo Dark and Soho Neon. These themes have a dark-themed embedded comment form to match the base color and it cannot be changed directly using the CSS on the post page.
So what if you have both the light-theme and dark-theme for the blog design? Which one should you pick for the base color of the embedded comment form to make it looks good for both theme?
Always Go With Light Theme
First, always go with light theme for the comment form base color. The reason is that you can apply CSS filters to dim the container element to make it blends well in dark theme. The reverse, however, requires more trial and error to find the right color composition.
Reduce the Brightness
When the dark theme is enabled, reduce the brightness of the comment form container. This should make it less straining for the eye.
/* this snippet use the default comment form selectors */
.comment-replybox-single:not(:empty),
.comment-replybox-thread:not(:empty),
.comments.embed .comment-form {
filter: brightness(0.95);
}