Add back noise texture

Add back the noise texture background by embedding the image file and setting it
as base64-encoded data as CSS background image.

data/data.go

@@ -2,6 +2,8 @@ package data
 
 import (
 	_ "embed"
+	"encoding/base64"
+	"strings"
 )
 
 //go:embed ui/window.ui
@@ -30,3 +32,12 @@ var LibraryPanelXML string
 
 //go:embed gtk.css
 var MainCSS string
+
+//go:embed noise-texture.png
+var NoiseTexture []byte
+
+func BuildMainCSS() string {
+	noiseTextureEncoded := "data:image/png;base64," + base64.StdEncoding.EncodeToString(NoiseTexture)
+
+	return strings.ReplaceAll(MainCSS, "@NOISETEXTURE@", noiseTextureEncoded)
+}