use variables in soft_media module

modules/readmes/soft_media.txt

@@ -2,5 +2,11 @@ in the css
 
 	@import url("https://styles.alv.cx/modules/soft_media.css");
 
+variables:
+
+	--soft-media-opacity: 0.75;
+	--soft-media-transition-time: .5s;
+	--soft-media-transition-timing-function: ease-in-out;
+
 this module makes reduces the opacity of all images to give the webpage a softer look,
 even when in light mode (this is default behaviour in dark mode).