Secondary action buttons color

[Klona13]

On top of the modification done:

• Opacity should be increased from 0.3 to 0.65 to increase some attention to them. They are a little harder to see in lighter modes.
• Since sepia flashback theme is the only dark theme with black text on these buttons, it will also get 20+ more lightness on top of the point above.
• Metropolis and Robotic themes have a hue shift for the button, it makes it look purple and pink on their themes respectively.
• Also to further simplify things a bit, burger menu button should use the same color as the secondary action buttons.