Link unit snippet to the unit page.

We use absolute links because the relative links of snippets only resolve when clicked, so the link can point to different places if the snippet is included in pages in different paths.

docs/styles/snippets/color_css_syntax.md

@@ -1,4 +1,4 @@
-The legal values for `<COLOR>` are dependant on the [class `Color`][textual.color.Color] and include:
+The legal values for a [color](/styles/css_units/color.md) depend on the [class `Color`][textual.color.Color] and include:
 
  - a recognised [named color](../../api/color#textual.color--named-colors) (e.g., `red`);
  - a hexadecimal number representing the RGB values of the color (e.g., `#F35573`);

docs/styles/snippets/fractional_syntax.md

@@ -1,4 +1,4 @@
-A fractional value can be set to
+A [fractional](/styles/css_units/fractional) value can be set to
 
  - a float between 0 and 1 (e.g., `0.45`); or
  - a percentage between 0% and 100% (e.g., `45%`).

docs/styles/snippets/percentage_syntax.md

@@ -1,2 +1,2 @@
-A percentage is a number followed by the percent sign.
+A [percentage](/styles/css_units/percentage) is a number followed by the percent sign.
 The number doesn't have to be an integer and values are clamped between 0% and 100%.

docs/styles/snippets/scalar_syntax.md

@@ -1,4 +1,4 @@
-A scalar can be any of the following:
+A [scalar](/styles/css_units/scalar) can be any of the following:
 
  - a fixed number of cells (e.g., `10`);
  - a fractional proportion relative to the sizes of the other widgets (e.g., `1fr`);