In 3.2-3.4 the built in sass compiler would throw an exception if it couldnt compile, and would allow a theme developer to see what the error was and what line in the browser. However in 3.5 it now calls the function debugging which leaves the browser showing the site without any styling at all and gives very little indication as to what the issue was, its only when checking the error_log that a theme dev will know what and where the scss failed to compile.

I think this is a bug because if the 
define('NO_DEBUG_DISPLAY', true); line in theme/styles.php is commented out, the debug message still doesn't appear.
 
The try catch in lib/outputlib.scss on line 1478 was changed in 3.5 from 
 
} catch (\Leafo\ScssPhp\Exception $e) {
 
to 
 
} catch (\Exception $e) {