add opacity to xresources and set default val to 0.9

config.def.h

@@ -94,7 +94,7 @@ char *termname = "st-256color";
 unsigned int tabspaces = 8;
 
 /* bg opacity */
-float alpha = 0.8;
+float alpha = 0.9;
 
 /* Terminal colors (16 first used in escape sequence) */
 static const char *colorname[] = {
@@ -214,6 +214,7 @@ ResourcePref resources[] = {
 		{ "borderpx",     INTEGER, &borderpx },
 		{ "cwscale",      FLOAT,   &cwscale },
 		{ "chscale",      FLOAT,   &chscale },
+		{ "opacity",	  FLOAT,   &alpha },
 };
 
 /*