Rename fields in ThemeColors (#3242)

This PR applies a number of field renames in the `ThemeColors` struct
from the `import-theme` branch.

This will help prevent this branch from diverging too far from `main`.

Release Notes:

- N/A

---------

Co-authored-by: Nate Butler <iamnbutler@gmail.com>
Co-authored-by: Marshall Bowers <1486634+maxdeviant@users.noreply.github.com>

crates/ui2/src/components/palette.rs

@@ -47,7 +47,7 @@ impl Palette {
             .id(self.id.clone())
             .w_96()
             .rounded_lg()
-            .bg(cx.theme().colors().elevated_surface)
+            .bg(cx.theme().colors().elevated_surface_background)
             .border()
             .border_color(cx.theme().colors().border)
             .child(
@@ -56,7 +56,12 @@ impl Palette {
                     .child(v_stack().py_0p5().px_1().child(div().px_2().py_0p5().child(
                         Label::new(self.input_placeholder.clone()).color(LabelColor::Placeholder),
                     )))
-                    .child(div().h_px().w_full().bg(cx.theme().colors().element))
+                    .child(
+                        div()
+                            .h_px()
+                            .w_full()
+                            .bg(cx.theme().colors().element_background),
+                    )
                     .child(
                         v_stack()
                             .id("items")