Update guides/theming.md

Co-authored-by: Jeremy Elbourn <[email protected]>

guides/theming.md

@@ -245,7 +245,7 @@ Angular Material themes are divided along several dimensions:
 Base
 : Common base styles for the design system. These styles don't change based on your configured
 colors, typography, or density, so they only need to be included once per application. These
-styles may include things such as border-radius, border-width, etc. All components have a base
+mixins include structural styles such as border-radius, border-width, etc. All components have a base
 mixin that can be used to include its base styles. (For example,
 `@include mat.checkbox-base($theme)`)