Can we have css or scss for the menu ?

Hi Romain,
 
It’s pity that our UB Mega Menu module only supports LESS as per Magento core. 
 
If you want to implement CSS, you can follow steps below: 

Step1: Copy the file: app\code\Ubertheme\UbMegaMenu\view\frontend\web\css\source\_module.less to app\design\frontend\YOUR_BRANCH\YOUR_THEME_NAME\Ubertheme_UbMegaMenu\web\css\source\_module.less
 
Step 2: Open the file: app\design\frontend\YOUR_BRANCH\YOUR_THEME_NAME\Ubertheme_UbMegaMenu\web\css\source\_module.less, add new code below at the bottom of the file:

@import ‘module/_style.css’;

 
Step 3: Under the folder: app\design\frontend\YOUR_BRANCH\YOUR_THEME_NAME\Ubertheme_UbMegaMenu\web\css\source\module\ and create a file name: _style.css
 
This is the file where you can define your own CSS. 
 
Please note, after you edit or add new changes to the css, you need to recompile LESS -> CSS following steps below:

You should back up your site first. Once done, you access your server via SSH and navigate to your Magento 2 folder, then run the following commands one by one:
Step 1: php bin/magento maintenance:enable
Step 2: rm -rf var/di/* var/generation/* var/cache/* var/log/* var/page_cache/* var/session/* var/view_preprocessed/* pub/static/frontend/YOUR_BRANCH/YOUR_THEME_NAME/*
Step 3: php bin/magento setup:static-content:deploy -t YOUR_BRANCH/YOUR_THEME_NAME -language sl_SI -f (Make sure you are using developer (or default) mode)
Step 4: php bin/magento cache:flush
step 5: php bin/magento maintenance:disable
Step 6: clear your browser cache

Hope that helps.
Best Regards,
Ziven.