Add support for HSL and HSLA

sandbox/hsl.py

@@ -0,0 +1,11 @@
+from textual.app import App, ComposeResult
+from textual.widgets import Static
+
+
+class HSLApp(App):
+    def compose(self) -> ComposeResult:
+        yield Static(classes="box")
+
+
+app = HSLApp(css_path="hsl.scss", watch_css=True)
+app.run()

sandbox/hsl.scss

@@ -0,0 +1,5 @@
+.box {
+  height: 1fr;
+  /*background: rgb(180,50, 50);*/
+  background: hsl(180,50%, 50%);
+}