t/ckeditor5/810: Made the link form buttons thicker with a fill color and no background.

[oleq]

Suggested merge commit message (convention)

Feature: Made the link form buttons thicker with a fill color and no background (see ckeditor/ckeditor5#810).

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Requires:

1. t/ckeditor5/810: Made the check and cancel icons thicker and fill-friendly. ckeditor5-core#125
2. t/ckeditor5/810: Made the link form buttons thicker with a fill color and no background. ckeditor5-theme-lark#161

[oleq]

Retina

Non-retina

[scofalik]

Just a small thing but could we put those icons a bit closer to each other? So the gap between them is same as gaps between field and icon, or icon and tooltip border. If it is just padding (no margins) then I guess we can't. IDK. Just my 5 cents, it was bothering me :P

[oleq]

@scofalik We cannot because it's a framework not a patchwork :P

[scofalik]

Yeah that's what I thought. Bummer.

[oleq]

I found out I slightly exaggerated the thickness. I updated the icons:

Retina

Non-retina