Expose more styling attributes

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At the moment, as style attributes we have:

• for Button: button_color, font_weight
• for Description: description_width

• some specifics for Slider, IntSlider and Progress, and ToggleButtons

Nothing at all for Text and other text inputs, ToggleButton, Checkbox .. and very little for Button finally.

We @LRI and Sagemath community, would very much like:

• text color, style and weight ; background color
• background images (supporting at least PNG and SVG)
• an image/icon in control text or description
• border-right/left/top/bottom

[tonywang531]

If I may add, there is no way to specify the width for the actual content except by defining total length. Also the tab length is fixed at 150 pixels which is easily exceeded with even a few words. I understand that the widgets are meant to be a minimalist UI approach, however I am currently stuck with this option as it is the integral part of interactive notebook.

In term of design choices, be able to set up mega menu, drop down with multiple field would be the dream. It would make everything looks much more concise.

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@tonywang531 what exactly do you mean with "set up" mega menu, drop down .. ?

[tonywang531]

@tonywang531 what exactly do you mean with "set up" mega menu, drop down .. ?

Please refer to the drop down and pop up menu here. Sorry I could not find the proper name for it.
https://semantic-ui.com/collections/menu.html

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3 PRs to address the first task

text color, style and weight ; background color

• for buttons: Styling buttons, text inputs, bool inputs. Raw CSS attributes. #2728
• for text inputs: Styling labels and text inputs #2729
• for booleans (incl. ToggleButton): Styling Button, Label, Text, Textarea, Combobox,ToggleButton, Checkbox & Valid.Adapted CSS attributes. #2730