Fixes second issue filed under #617 https://github.com/zsh-users/zsh-syntax-highlighting/issues/617#issuecomment-551253422 In the case of a command substitution in an alias, $arg[i,end_pos] would not pass to the end of $arg and i <= start_pos - end_pos would not iterate over all of $arg. Use $arg[i,-1] and $#arg respectively to avoid issues in aliases.
zsh-syntax-highlighting / highlighters
Navigate into the individual highlighters' documentation to see
what styles ($ZSH_HIGHLIGHT_STYLES keys) each highlighter defines.
Refer to the documentation on highlighters for further information.