Mobile navigation menu is not correct at 767 width

Problem/Motivation

With a width of 767 pixels, after clicking on the hamburger, the menu reopens.

Steps to reproduce

1. Install "base_zymphonies_theme" and set it as default.
2. Change the resolution to 767px.
3. Click on the hamburger
4. The menu is always reopened

Proposed resolution

1. In the media.scss file, change the rule @media (min-width: 767px) {....} to @media (min-width: 768px) {....}
2. rebuild project to compile style

Remaining tasks

- None

User interface changes

- None

API changes

- None

Data model changes

- None