Visual design: Update Zoom +/- icons to be white (vs black)

[mareekuh]

Can we make the glyphs for the +/- zoom icons be white instead of black.
This way they better fit with the rest of the app and they will be in line with what PVA has

(PVA)
(ours)

[vivekkshankar]

@mareekuh sure, it does stick out. I agree.

For context here are the reasons for the grey:

• Allows us to make it a transparent layer so one can see behind.
• Helps us create sufficient contrast with the backgroud.
• Avoids having multiple z levels and similar looking UI elements in the canvas i.e the nodes themselves.

P.S Looks like PVA made a change we didnt catch up with. They were dark grey too until recently.