Generate SVG turbulence noise textures for grainy overlays.
background-image: url("data:image/svg+xml,%3Csvg%20xmlns%3D'http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg'%20width%3D'200'%20height%3D'200'%3E%3Cfilter%20id%3D'n'%3E%3CfeTurbulence%20baseFrequency%3D'0.8'%20numOctaves%3D'3'%2F%3E%3C%2Ffilter%3E%3Crect%20width%3D'100%25'%20height%3D'100%25'%20filter%3D'url(%2523n)'%20opacity%3D'0.5'%2F%3E%3C%2Fsvg%3E");