UI improvements

[Senyoret1]

Did you run make format && make check?
The go code was not changed. npm run lint and npm run build were used.

Changes:

• A new button for changing the tabs in small screens was added, as the old UI for tabs was not adecuate.

Before:

After:

• The style for buttons under the modal window title was standarized.

• Various other minor improvements.

How to test this PR:
Open the modal window for configuring the vpn-client in a phone or small browser window. You will be able to change the current tab using the button.