Improve CSS syntax highlighting (#25326)

Release Notes:

  - Improved CSS syntax highlighting

| Zed 0.174.6 | With this PR |
| --- | --- |
| ![css_0 174
6](https://github.com/user-attachments/assets/d069f20e-5f1f-4d03-a010-81ba4b61b3a0)
|
![css_pr](https://github.com/user-attachments/assets/36463ef1-2ead-421d-9825-bd359e7677ab)
|

- `|`: `operator`
- `and`, `or`, `not`, `only`: `operator` -> `keyword.operator`, as
defined in other languages
- `id_name`, `class_name`: `property`/`attribute` -> `selector`, not a
property name. [CSS
reference](https://www.w3.org/TR/selectors-3/#class-html)
- `namespace_name`: `property` -> `namespace`, not a property name
- `property_name`: `constant` -> `property`, like `feature_name` already
defined
- `(keyword_query)`: `property`, similar to `feature_name`. [CSS
reference](https://www.w3.org/TR/mediaqueries-3/#media1)
- `keyword_query`: `constant.builtin`, [CSS
reference](https://www.w3.org/TR/mediaqueries-3/#media0)
- `plain_value`, `keyframes_name`: `constant.builtin`, [CSS
reference](https://www.w3.org/TR/css-values-3/#value-defs)
- `unit`: `type` -> `type.unit`,
[Atom](9e4afce058/grammars/tree-sitter-css.cson (L73))
and [VS
Code](336801752d/extensions/css/syntaxes/css.tmLanguage.json (L1393))
also have a `unit` scope for this. [CSS
reference](https://www.w3.org/TR/css3-values/#dimensions)


```css
@media (keyword_query) and keyword_query {}
@supports (feature_name: plain_value) {}
@namespace namespace_name url("string");
namespace_name|tag_name {}
@keyframes keyframes_name {
  to {
    top: 200unit;
    color: #c01045;
  }
}
tag_name::before,
#id_name:nth-child(even),
.class_name[attribute_name=plain_value] {
  property_name: 2em 1.2em;
  --variable: rgb(250, 0, 0);
  color: var(--variable);
  animation: keyframes_name 5s plain_value;
}
```

assets/themes/ayu/ayu.json

@@ -261,6 +261,11 @@
             "font_style": null,
             "font_weight": null
           },
+          "namespace": {
+            "color": "#bfbdb6ff",
+            "font_style": null,
+            "font_weight": null
+          },
           "number": {
             "color": "#d2a6ffff",
             "font_style": null,
@@ -316,6 +321,16 @@
             "font_style": null,
             "font_weight": null
           },
+          "selector": {
+            "color": "#d2a6ffff",
+            "font_style": null,
+            "font_weight": null
+          },
+          "selector.pseudo": {
+            "color": "#5ac1feff",
+            "font_style": null,
+            "font_weight": null
+          },
           "string": {
             "color": "#a9d94bff",
             "font_style": null,
@@ -632,6 +647,11 @@
             "font_style": null,
             "font_weight": null
           },
+          "namespace": {
+            "color": "#5c6166ff",
+            "font_style": null,
+            "font_weight": null
+          },
           "number": {
             "color": "#a37accff",
             "font_style": null,
@@ -687,6 +707,16 @@
             "font_style": null,
             "font_weight": null
           },
+          "selector": {
+            "color": "#a37accff",
+            "font_style": null,
+            "font_weight": null
+          },
+          "selector.pseudo": {
+            "color": "#3b9ee5ff",
+            "font_style": null,
+            "font_weight": null
+          },
           "string": {
             "color": "#86b300ff",
             "font_style": null,
@@ -1003,6 +1033,11 @@
             "font_style": null,
             "font_weight": null
           },
+          "namespace": {
+            "color": "#cccac2ff",
+            "font_style": null,
+            "font_weight": null
+          },
           "number": {
             "color": "#dfbfffff",
             "font_style": null,
@@ -1058,6 +1093,16 @@
             "font_style": null,
             "font_weight": null
           },
+          "selector": {
+            "color": "#dfbfffff",
+            "font_style": null,
+            "font_weight": null
+          },
+          "selector.pseudo": {
+            "color": "#72cffeff",
+            "font_style": null,
+            "font_weight": null
+          },
           "string": {
             "color": "#d4fe7fff",
             "font_style": null,