Show background decoration at every width

The gradients, sphere, glows, wave artwork and G-code were hidden below
the 1024px breakpoint, so narrow or zoomed browser windows got a plain
black page. Add stacked-layout variants of the decoration and lower the
full-design breakpoint to 960px.

tailwind.config.js

@@ -2,6 +2,7 @@ module.exports = {
   content: ["./src/**/*.pug"],
   theme: {
     extend: {
+      screens: { lg: "960px" },
       colors: {
         accent: "#5272d3",
         deep: "#15164e",