Windows/css keywords

core/src/toga/style/pack.py

@@ -7,6 +7,7 @@
     from travertino.colors import rgb, hsl
 
 from travertino.constants import (  # noqa: F401
+    ABSOLUTE_FONT_SIZES,
     BOLD,
     BOTTOM,
     CENTER,
@@ -23,6 +24,7 @@
     NONE,
     NORMAL,
     OBLIQUE,
+    RELATIVE_FONT_SIZES,
     RIGHT,
     ROW,
     RTL,
@@ -107,7 +109,12 @@ class IntrinsicSize(BaseIntrinsicSize):
     font_style: str = validated_property(*FONT_STYLES, initial=NORMAL)
     font_variant: str = validated_property(*FONT_VARIANTS, initial=NORMAL)
     font_weight: str = validated_property(*FONT_WEIGHTS, initial=NORMAL)
-    font_size: int = validated_property(integer=True, initial=SYSTEM_DEFAULT_FONT_SIZE)
+    font_size: int | str = validated_property(
+        *ABSOLUTE_FONT_SIZES,
+        *RELATIVE_FONT_SIZES,
+        integer=True,
+        initial=SYSTEM_DEFAULT_FONT_SIZE,
+    )
 
     @classmethod
     def _debug(cls, *args: str) -> None:  # pragma: no cover
@@ -930,7 +937,13 @@ def __css__(self) -> str:
             else:
                 css.append(f"font-family: {self.font_family};")
         if self.font_size != SYSTEM_DEFAULT_FONT_SIZE:
-            css.append(f"font-size: {self.font_size}pt;")
+            if isinstance(self.font_size, str) and (
+                self.font_size in ABSOLUTE_FONT_SIZES
+                or self.font_size in RELATIVE_FONT_SIZES
+            ):
+                css.append(f"font-size: {self.font_size};")
+            else:
+                css.append(f"font-size: {self.font_size}pt;")
         if self.font_weight != NORMAL:
             css.append(f"font-weight: {self.font_weight};")
         if self.font_style != NORMAL:

travertino/src/travertino/constants.py

@@ -108,6 +108,24 @@
 
 RELATIVE_FONT_SIZES = {LARGER, SMALLER}
 
+FONT_SIZE_SCALE_FACTOR = 1.2
+
+FONT_SIZE_SCALE = {
+    XX_SMALL: 0.512,  # ~(1/FONT_SIZE_SCALE_FACTOR)^3 - 60% smaller
+    X_SMALL: 0.64,  # ~(1/FONT_SIZE_SCALE_FACTOR)^2 - 40% smaller
+    SMALL: 0.8,  # ~(1/FONT_SIZE_SCALE_FACTOR) - 20% smaller
+    MEDIUM: 1.0,  # baseline
+    LARGE: 1.2,  # ~FONT_SIZE_SCALE_FACTOR - 20% larger
+    X_LARGE: 1.44,  # ~FONT_SIZE_SCALE_FACTOR^2 - 40% larger
+    XX_LARGE: 1.728,  # ~FONT_SIZE_SCALE_FACTOR^3 - 60% larger
+    XXX_LARGE: 2.074,  # ~FONT_SIZE_SCALE_FACTOR^4 - 80% larger
+}
+
+RELATIVE_FONT_SIZE_SCALE = {
+    LARGER: FONT_SIZE_SCALE_FACTOR,  # 20% larger
+    SMALLER: 1 / FONT_SIZE_SCALE_FACTOR,  # 20% smaller
+}
+
 ######################################################################
 # Colors
 ######################################################################

travertino/src/travertino/fonts.py

@@ -1,11 +1,13 @@
 from .constants import (
+    ABSOLUTE_FONT_SIZES,
     BOLD,
     FONT_STYLES,
     FONT_VARIANTS,
     FONT_WEIGHTS,
     ITALIC,
     NORMAL,
     OBLIQUE,
+    RELATIVE_FONT_SIZES,
     SMALL_CAPS,
     SYSTEM_DEFAULT_FONT_SIZE,
 )
@@ -26,6 +28,11 @@ def __init__(self, family, size, style=NORMAL, variant=NORMAL, weight=NORMAL):
             try:
                 if size.strip().endswith("pt"):
                     self.size = int(size[:-2])
+                elif (
+                    size.strip() in ABSOLUTE_FONT_SIZES
+                    or size.strip() in RELATIVE_FONT_SIZES
+                ):
+                    self.size = size.strip()
                 else:
                     raise ValueError(f"Invalid font size {size!r}")
             except Exception:
@@ -47,7 +54,9 @@ def __repr__(self):
             (
                 "system default size"
                 if self.size == SYSTEM_DEFAULT_FONT_SIZE
-                else f"{self.size}pt"
+                else (
+                    f"{self.size}" if isinstance(self.size, str) else f"{self.size}pt"
+                )
             ),
             self.family,
         )

travertino/tests/test_fonts.py

@@ -1,12 +1,24 @@
 import pytest
 
 from travertino.constants import (
+    ABSOLUTE_FONT_SIZES,
     BOLD,
     ITALIC,
+    LARGE,
+    LARGER,
+    MEDIUM,
     NORMAL,
     OBLIQUE,
+    RELATIVE_FONT_SIZES,
+    SMALL,
     SMALL_CAPS,
+    SMALLER,
     SYSTEM_DEFAULT_FONT_SIZE,
+    X_LARGE,
+    X_SMALL,
+    XX_LARGE,
+    XX_SMALL,
+    XXX_LARGE,
 )
 from travertino.fonts import Font
 
@@ -79,10 +91,64 @@ def test_simple_construction(size):
     assert_font(Font("Comic Sans", size), "Comic Sans", 12, NORMAL, NORMAL, NORMAL)
 
 
+@pytest.mark.parametrize(
+    "size",
+    [
+        XX_SMALL,
+        X_SMALL,
+        SMALL,
+        MEDIUM,
+        LARGE,
+        X_LARGE,
+        XX_LARGE,
+        XXX_LARGE,
+        LARGER,
+        SMALLER,
+    ],
+)
+def test_css_font_size_keywords(size):
+    font = Font("Comic Sans", size)
+    assert_font(font, "Comic Sans", size, NORMAL, NORMAL, NORMAL)
+    assert isinstance(font.size, str)
+    assert font.size in ABSOLUTE_FONT_SIZES or font.size in RELATIVE_FONT_SIZES
+
+
+@pytest.mark.parametrize(
+    "size, expected_repr",
+    [
+        (XX_SMALL, "<Font: xx-small Comic Sans>"),
+        (X_SMALL, "<Font: x-small Comic Sans>"),
+        (SMALL, "<Font: small Comic Sans>"),
+        (MEDIUM, "<Font: medium Comic Sans>"),
+        (LARGE, "<Font: large Comic Sans>"),
+        (X_LARGE, "<Font: x-large Comic Sans>"),
+        (XX_LARGE, "<Font: xx-large Comic Sans>"),
+        (XXX_LARGE, "<Font: xxx-large Comic Sans>"),
+        (LARGER, "<Font: larger Comic Sans>"),
+        (SMALLER, "<Font: smaller Comic Sans>"),
+    ],
+)
+def test_css_font_size_repr(size, expected_repr):
+    font = Font("Comic Sans", size)
+    assert repr(font) == expected_repr
+
+
 def test_invalid_construction():
     with pytest.raises(ValueError):
         Font("Comic Sans", "12 quatloos")
 
+    with pytest.raises(ValueError):
+        Font("Comic Sans", "invalid-size")
+
+    with pytest.raises(ValueError):
+        Font("Comic Sans", "")
+
+    try:
+        Font("Comic Sans", None)
+        assert False, "Should have raised TypeError"
+    except TypeError:
+        pass
+
 
 @pytest.mark.parametrize(
     "family",

winforms/src/toga_winforms/fonts.py

@@ -91,6 +91,8 @@ def __init__(self, interface):
                 font_style |= FontStyle.Italic
 
             # Convert font size to Winforms format
+            # TODO: update font-size to include CSS keywords
+            # size such as small, medium, and large.
             if self.interface.size == SYSTEM_DEFAULT_FONT_SIZE:
                 font_size = DEFAULT_FONT.Size
             else: