* Replace a Sass variable with a CSS custom property - $container-gap-width
* Replace a Sass variable with a CSS custom property - $container-border-width
This PR adds the flex declaration to mx_RoomHeader_button to prevent the buttons from being compressed due to a long room name, copying the whole declarations from mx_RightPanel_headerButton for reference.
Signed-off-by: Suguru Hirahara <luixxiul@users.noreply.github.com>