Add tooltips/alt-text for mobile UI buttons

[JKSH]

When composing a New Topic on a mobile screen (or a desktop when the browser window size is small), the "Discard", "Minimize", and "Submit" buttons are shown on the top bar as icons: X, -, and >.

It would be helpful for these icons to get tooltips/alt-text for accessibility and for users who aren't familiar with the meanings of these icons.

[dunlix]

@jksh I agree. You could add these yourself to your Forum with editing of the templates/themes, but I'm not very good at that. Maybe change the text with Custom CSS/JS?