feat: the selected row is a shade of the terminal's background

lazysecrets asks the terminal for its background and shades the
selection from it, a little lighter on a dark background and darker on
a light one, where palette 8 was often too bright to read coloured rows
on. Palette 8 stays until the terminal answers, or if it doesn't, and
a theme's selection colours still win.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

internal/ui/styles/styles.go

@@ -3,6 +3,8 @@
 package styles
 
 import (
+	"image/color"
+
 	"charm.land/lipgloss/v2"
 
 	"git.kebcloud.no/keb/lazysecrets/internal/provider"
@@ -32,6 +34,10 @@ type Styles struct {
 	KindAzure      lipgloss.Style
 	KindDatabricks lipgloss.Style
 	KindRepo       lipgloss.Style
+
+	// themed marks the selection colours as set by the theme, so
+	// OnBackground leaves them.
+	themed, themedBlurred bool
 }
 
 func Default() Styles {
@@ -45,7 +51,8 @@ func Default() Styles {
 
 		// A background rather than reverse, so the row keeps its colours;
 		// in every pane, so each shows what's selected in it. The focused
-		// pane's is bold too.
+		// pane's is bold too. Palette 8 until the terminal says what its
+		// background is (OnBackground).
 		Selected:        lipgloss.NewStyle().Background(lipgloss.BrightBlack).Bold(true),
 		SelectedBlurred: lipgloss.NewStyle().Background(lipgloss.BrightBlack),
 		Muted:           lipgloss.NewStyle().Faint(true),
@@ -76,3 +83,23 @@ func (s Styles) Kind(k provider.Kind) lipgloss.Style {
 	}
 	return s.KindAzure
 }
+
+// OnBackground shades the selection colours from the terminal's
+// background, a little lighter on a dark one and darker on a light one:
+// a quiet band that keeps the row's colours readable, where palette 8 is
+// often too bright. Colours the theme sets are kept.
+func (s Styles) OnBackground(bg color.Color, dark bool) Styles {
+	shade := func(p float64) color.Color {
+		if dark {
+			return lipgloss.Lighten(bg, p)
+		}
+		return lipgloss.Darken(bg, p)
+	}
+	if !s.themed {
+		s.Selected = s.Selected.Background(shade(0.09))
+	}
+	if !s.themedBlurred {
+		s.SelectedBlurred = s.SelectedBlurred.Background(shade(0.05))
+	}
+	return s
+}