You can install the light or regular version for 99 dollars per year in your style. Only the solid icons are free.
Not all, but some look bad. Some are much too big - you have to scale down in the css. A new icon that I added to the navbar today, I had to enlarge it and configure it completely different. Some of the old icons of the forums & topic icons I had to replace. Also you have to make them smaller. An icon that I had inserted in the lastsubject is no longer displayed correctly.
Three days for updating 3 styles and still not finished. In some styles it is like a bottomless pit.
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Edit: 26.06.
Even if nothing more should be written here concerning the icons:
I think it's an absolutely no-go if you have to format every icon differently in size if you want to insert them as forum & topic icons in style. This is caused by a mixture of old and new icons, I think
(or because in the css you cannot choose fab, fa, fas, far but only font-size normal or font-size: 900;).
Just now the Simple-3D installed in TB. The forum icons in the index vary from 20-24px now. But this way I find the appearance to be suitable.
Until 3.3.0, all these icons had one size and they looked good. Now, even some icons inserted into the html must be adapted, enlarged or reduced in the style.css.
Besides: what if a user wants to insert a completely different icon...