- Ximper linux branding

To the pity, it seems there is currently no way to alter the color
that is used to highlight the currently selected option:

* https://stackoverflow.com/questions/17698110/how-to-change-color-of-selection-in-select-option

* https://stackoverflow.com/questions/26392014/change-color-of-selected-option-in-html-select-input

The horizontal paddings of a table cell and of the input inside it
aren't combined properly resulting in inputs that are wider than the
surrounding cell.

Some buttons should be wider in accordance with their text.