fix(style): Fix regressions introduced by #2338 (#2345)

Put Column Slim Back Button classnames in order so it is positioned right and top. Add icon button style back to privacy dropdown and upload buttons so they are positioned correctly and do not wiggle. Remove abstracted style from CSS. Add missed class for the upload form thumbnail. Add the missed styles for upload form thumnail. Alphabetize styles for column-back-button. Fix fontSize typo for media-spoiler-video-play-icon.