Re: Bold
They all look the same in that test you posted.
Windows 10 Pro 64
Tried Firefox, Chrome and Edge
Light theme.
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So it could be that the font isn’t loading and perhaps you already have it installed.
Looking closer:
It claims to be Helvetica, Arial, sans-serif;
Bold weight: 400 (which is normally for regular)
Regular weight: 300 (which is normally light)
But most people wont have a 300 weight of those I’d imagine.
I’m a graphic designer and even I don’t have them. (I have Helvetica Neue which doesn’t load instead).
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So I would pick a google font and embed it – Open Sans, Roboto, Lato, etc.
Otherwise keep away from font-weight: 300