cssColorArgb function
Formats an ARGB integer as lowercase CSS hexadecimal.
Opaque colors use #rrggbb; colors carrying alpha use #rrggbbaa,
following CSS ordering rather than the input integer's ARGB ordering.
Implementation
String cssColorArgb(int argb) {
final rgb = (argb & 0xFFFFFF).toRadixString(16).padLeft(6, '0');
final alpha = (argb >> 24) & 0xFF;
return alpha == 0xFF
? '#$rgb'
: '#$rgb${alpha.toRadixString(16).padLeft(2, '0')}';
}