Update use of Sass variable background variant colors

The hardcoded Sass variable assignments to lighter variant background colors
does not work well with the theme-color functions that are used.

Use Bootstrap's built in theme-color-level function to programatically get
a lighter variant color to use for component backgrounds.

https://getbootstrap.com/docs/4.5/getting-started/theming/#functions

Signed-off-by: Yoshie Muranaka <yoshiemuranaka@gmail.com>
Change-Id: I9d5a1a66c92d347ba1797be5e0810a24c34094f9
diff --git a/src/assets/styles/bmc/helpers/_index.scss b/src/assets/styles/bmc/helpers/_index.scss
index e4abf9c..ce0631a 100644
--- a/src/assets/styles/bmc/helpers/_index.scss
+++ b/src/assets/styles/bmc/helpers/_index.scss
@@ -1,3 +1,4 @@
 @import "./colors";
 @import "./motion";
-@import "./variables";
\ No newline at end of file
+@import "./variables";
+@import "./functions";
\ No newline at end of file