tailwind: upgrade a17t, somewhat functional dark mode

instead of adding dark: variants to each element, a preprocessor script
adds them. still needs to be implemented to typescript.

scripts/dark-variant.sh

@@ -0,0 +1,7 @@
+#!/bin/bash
+
+for f in $1/*.html; do
+    for color in neutral positive urge warning info critical; do
+        sed -i "s/~${color}/~${color} dark:~d_${color}/g" $f
+    done
+done