editor: Ensure that spacer blocks are visible in light themes (#48287)

Dino created 

The color used for the slash pattern when rendering `Block::Spacer` was
set to a fixed color, `0xFFFFFF10`, which is almost white, making it
super hard to view in light themes, where the editor's background is
almost white.

As such, this commit updates that color so as to use something that is
more theme-specific, ensuring that it is easily visible in both light
and dark themes.

Release Notes:

- N/A

Change summary

crates/editor/src/element.rs | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

Detailed changes

crates/editor/src/element.rs 🔗 

@@ -49,8 +49,8 @@ use gpui::{
     Pixels, PressureStage, ScrollDelta, ScrollHandle, ScrollWheelEvent, ShapedLine, SharedString,
     Size, StatefulInteractiveElement, Style, Styled, StyledText, TextAlign, TextRun,
     TextStyleRefinement, WeakEntity, Window, anchored, deferred, div, fill, linear_color_stop,
-    linear_gradient, outline, pattern_slash, point, px, quad, relative, rgba, size,
-    solid_background, transparent_black,
+    linear_gradient, outline, pattern_slash, point, px, quad, relative, size, solid_background,
+    transparent_black,
 };
 use itertools::Itertools;
 use language::{IndentGuideSettings, language_settings::ShowWhitespaceSetting};
@@ -4005,7 +4005,11 @@ impl EditorElement {
                 .id(block_id)
                 .w_full()
                 .h((*height as f32) * line_height)
-                .bg(pattern_slash(rgba(0xFFFFFF10), 8.0, 8.0))
+                .bg(pattern_slash(
+                    cx.theme().colors().panel_background,
+                    8.0,
+                    8.0,
+                ))
                 .into_any(),
         };