see if a rename helps

app/assets/stylesheets/theme1/_theme_structure.css.sass

@@ -1,4 +1,3 @@
-$cth-height: 48px
 =linear-gradient($pos, $G1, $G2: null, $G3: null, $G4: null, $G5: null, $G6: null, $G7: null, $G8: null, $G9: null, $G10: null, $fallback: null)
   // Detect what type of value exists in $pos
   $pos-type: type-of(nth($pos, 1))

app/assets/stylesheets/theme1/application.css.sass

@@ -11,4 +11,4 @@ $font-family-content: Georgia, serif
 @import ./foundation_and_overrides
 @import ./elements/*
 @import ./pages/*
-@import ./structure
+@import ./theme_structure