Add a strip-units function to make sure every value is accepted (15…

… or 15px)

scss/_functions.scss

@@ -303,8 +303,12 @@ $_luminance-list: .0008 .001 .0011 .0013 .0015 .0017 .002 .0022 .0025 .0027 .003
 }
 
 // OUDS mod
+@function strip-units($value) {
+  @return divide($value, $value * 0 + 1)
+}
+
 @function px-to-rem($value) {
-  $rem-value: $value * .0625; // Assumes the browser default, typically `16px`
+  $rem-value: strip-units($value) * .0625; // Assumes the browser default, typically `16px`
   @return #{$rem-value}rem;
 }
 // End mod