Add GUI test for :target

src/test/rustdoc-gui/target.goml

@@ -0,0 +1,35 @@
+// Check that the targetted element has the expected styles.
+goto: "file://" + |DOC_PATH| + "/lib2/struct.Foo.html#method.a_method"
+show-text: true
+
+// Confirming that the method is the target.
+assert: "#method\.a_method:target"
+
+define-function: (
+    "check-style",
+    (theme, background, border),
+    [
+        ("local-storage", {"rustdoc-theme": |theme|, "rustdoc-use-system-theme": "false"}),
+        ("reload"),
+        ("assert-css", ("#method\.a_method:target", {
+            "background-color": |background|,
+            "border-right": "3px solid " + |border|,
+        })),
+    ],
+)
+
+call-function: ("check-style", {
+    "theme": "ayu",
+    "background": "rgba(255, 236, 164, 0.06)",
+    "border": "rgba(255, 180, 76, 0.85)",
+})
+call-function: ("check-style", {
+    "theme": "dark",
+    "background": "rgb(73, 74, 61)",
+    "border": "rgb(187, 116, 16)",
+})
+call-function: ("check-style", {
+    "theme": "light",
+    "background": "rgb(253, 255, 211)",
+    "border": "rgb(173, 124, 55)",
+})