Change background style target for tab icons

[artonge]

The style was applied to the containing element instead of the icon element.

Don't know why the background-position: center 8px; was needed, so I removed it. It was also shifting icons toward the bottom when applied to the icon.

Tested in styleguide.

Fix: nextcloud/activity#669
Problem introduced here: #1939

[skjnldsv]

Don't know why the background-position: center 8px; was needed,

To support the legacy icon methods iirc. But that changed when we added compatibility for the MaterialDesignIcons

[raimund-schluessler]

I am a bit puzzled why this only happens for the activity icon. All other icons in the files sidebar of c.nc.c are fine, although they also use the legacy icons and not material design.

But your changes fix the problem, so 👍

[raimund-schluessler]

I am a bit puzzled why this only happens for the activity icon. All other icon in the files sidebar of c.nc.c are fine, although they also use the legacy icons and not material design.

I found out what causes this. The activity icon specifies a width, height and viewBox of 32 px in the svg:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<svg xmlns="http://www.w3.org/2000/svg" height="32" width="32" version="1.0" viewBox="0 0 32 32">
 <path d="m16 1-10 18h11l-1 12 10-18h-11z" fill="#FFF"/>
</svg>

whereas all other icons only specify the (correct) size of 16px, e.g. spreed:

<svg width="16" height="16" version="1.1" viewBox="0 0 16 16" xmlns="http://www.w3.org/2000/svg">
<path d="m7.9992 0.999a6.9993 6.9994 0 0 0-6.9992 6.9996 6.9993 6.9994 0 0 0 6.9992 6.9994 6.9993 6.9994 0 0 0 3.6308-1.024c0.86024 0.34184 2.7871 1.356 3.2457 0.91794 0.47922-0.45765-0.56261-2.6116-0.81238-3.412a6.9993 6.9994 0 0 0 0.935-3.4814 6.9993 6.9994 0 0 0-6.9991-6.9993zm8e-4 2.6611a4.34 4.3401 0 0 1 4.34 4.3401 4.34 4.3401 0 0 1-4.34 4.3398 4.34 4.3401 0 0 1-4.34-4.3398 4.34 4.3401 0 0 1 4.34-4.3401z" fill="#fff" stroke-width=".14"/>
</svg>

So for the larger activity icon we have to explicitly set the size correctly.

[raimund-schluessler]

/backport to stable4