I type my text in LibreOffice and use Zotero to take care of the references. Zotero has a list of many different citation styles, which likely already includes the one for the journal you are submitting your manuscript to.
However, this may not always be the case. I had to use a citation style which was not available for Zotero and therefore needed to create it myself. Of course you can just create it from scratch using your favourite text editor. Well… you may be able to do that, but I am certainly not. Therefore I searched a bit and came across the Visual CSL Editor.
The first thing I had to do was to find a style that looks as close as possible to what I needed. After a lot of searching I finally found a style that was very similar (though not identical). It was called Vancouver and after searching it in the Find and edit CSL citation styles field, I was presented with the option to Edit the style:
Then you are presented with the editing options:
It took me a lot of time to make it look right and I really hope it takes you less! Meanwhile I renamed the style from STYLE INFO > Info to “Vancouver Custom 1”. When everything was ready I exported my customized style from Style > Save Style and selected Save to disk from the popup.
Then I imported it in Zotero.