Experiment with CSS filter for inline-colors

Inside darker inputs, some colors like dark blue will be hard to read, so we could try to improve text-color contrast with global adjustments depending on the theme.

ts/editable/editable-base.scss

@@ -18,6 +18,15 @@ p {
     display: none;
 }
 
+/* Nudge users towards using brighter colors,
+   so they are more readable in dark themes */
+span[style*="color"] {
+    filter: brightness(0.8);
+}
+
 :host(.night-mode) {
     @include scrollbar.night-mode;
+    span[style*="color"] {
+        filter: brightness(1.2);
+    }
 }