Improve Notebook styling

...Once we get PageWrapper, that is

internal/styles/fallback/wintergreen.go

@@ -9,6 +9,9 @@ import "git.tebibyte.media/tomo/tomo"
 import "git.tebibyte.media/tomo/tomo/event"
 import "git.tebibyte.media/tomo/backend/style"
 
+// Note: these are color.RGBA values. Remember alpha premultiplication.
+
+var colorTransparent           = color.RGBA {                         A: 0   }
 var colorFocus                 = color.RGBA { R:  61, G: 128, B: 143, A: 255 }
 var colorInput                 = color.RGBA { R: 208, G: 203, B: 150, A: 255 }
 var colorCarved                = color.RGBA { R: 151, G: 160, B: 150, A: 255 }
@@ -454,47 +457,41 @@ rules := []style.Rule {
 		tomo.AttrMinimumSize { X: 32, Y: 32 },
 		tomo.AttrColor { Color: colorCalendarWeekend },
 	), tomo.R("", "CalendarDay"), "weekend"),
+
+	// *.Notebook
+	style.Ru(style.AS (
+		tomo.AGap(0, 0),
+	), tomo.R("", "Notebook")),
+
+	// *.PageWrapper
+	style.Ru(style.AS (
+		tomo.ABorder (
+			tomo.Border {
+				Width: tomo.I(0, 1, 1, 1),
+				Color: borderColorOutline,
+			},
+			tomo.Border {
+				Width: tomo.I(0, 1, 1, 1),
+				Color: borderColorLifted,
+			}),
+		tomo.AColor(tomo.ColorBackground),
+		tomo.APadding(8),
+	), tomo.R("", "PageWrapper")),
 	
 	// *.TabRow
 	style.Ru(style.AS (
-		tomo.AttrBorder {
+		tomo.AGap(0, 0),
-			tomo.Border {
-				Width: tomo.I(1, 1, 0, 1),
-				Color: borderColorOutline,
-			},
-			tomo.Border {
-				Width: tomo.I(1, 0, 0, 1),
-				Color: borderColorEngraved,
-			},
-		},
-		tomo.AttrGap { X: 0, Y: 0 },
-		tomo.AttrColor { Color: colorGutter },
 		tomo.AttrPadding(tomo.I(1, 0, 0, 0)),
 	), tomo.R("", "TabRow")),
 	
-	// *.TabSpacer[left]
-	style.Ru(style.AS (
-		tomo.AttrBorder {
-			tomo.Border {
-				Width: tomo.I(0, 0, 1, 0),
-				Color: borderColorEngraved,
-			},
-			tomo.Border {
-				Width: tomo.I(0, 0, 1, 0),
-				Color: borderColorOutline,
-			},
-		},
-		tomo.AttrMinimumSize { X: 1 },
-	), tomo.R("", "TabSpacer")),
-	
 	// *.TabSpacer[right]
 	style.Ru(style.AS (
 		tomo.AttrBorder {
 			tomo.Border {
 				Width: tomo.I(1, 0, 0, 0),
 				Color: [4]color.Color {
-					colorGutter, colorGutter,
+					colorTransparent, colorTransparent,
-					colorGutter, colorGutter,
+					colorTransparent, colorTransparent,
 				},
 			},
 			tomo.Border {
@@ -505,10 +502,6 @@ rules := []style.Rule {
 				Width: tomo.I(0, 0, 1, 1),
 				Color: borderColorOutline,
 			},
-			tomo.Border {
-				Width: tomo.I(0, 0, 0, 1),
-				Color: borderColorShade,
-			},
 		},
 		tomo.AttrMinimumSize { X: 3 },
 	), tomo.R("", "TabSpacer"), "right"),
@@ -519,8 +512,8 @@ rules := []style.Rule {
 			tomo.Border {
 				Width: tomo.I(1, 0, 0, 0),
 				Color: [4]color.Color {
-					colorGutter, colorGutter,
+					colorTransparent, colorTransparent,
-					colorGutter, colorGutter,
+					colorTransparent, colorTransparent,
 				},
 			},
 			tomo.Border {