Use 35% opacity for faded elements in the network icons

Currently, I see that the network icons aren't visible enough. For example, I find it difficult to determine the signal strength of the network without peering. I would like these icons to be more visible, and therefore I propose to use 35% opacity for faded elements. As for me, this solution makes determining the signal level more convenient and the icons more informative.

See https://invent.kde.org/frameworks/plasma-framework/-/merge_requests/28