Don't show button outline when button isn't pressed

Increase the contrast of the icons/text on the button by having it be white
on black background instead of white on gray background.

This will be helpful when we introduce pixel shifting in the next few commits,
as now the off-centering of icons is going to be harder to notice.

Author: jonas2515

src/main.rs

@@ -36,7 +36,7 @@ use display::DrmBackend;
 
 const DFR_WIDTH: i32 = 2008;
 const DFR_HEIGHT: i32 = 64;
-const BUTTON_COLOR_INACTIVE: f64 = 0.200;
+const BUTTON_COLOR_INACTIVE: f64 = 0.0;
 const BUTTON_COLOR_ACTIVE: f64 = 0.400;
 const TIMEOUT_MS: i32 = 30 * 1000;