Can we extend the styles screen to add our own additional style elements?
This is not possible unfortunately because each underlying grid needs then to implement that style separately (and not all are DOM based and won't use CSS). If you would like to add extra properties to Conditional Styles that are not currently present please provide us with the details and we will try to add them in a future release.
Can we provide the name of a css style instead of building it?
Yes, you can do that. When you create a predefined Conditional Style there is a StyleName property which you can use to provide the name of the css style. If you do that, then its your responsibility to ensure that style is available in your css. Additionally, you can provide a list of styles in UserInterface config adn then they will be available in a dropdown in the Conditional Styles wizard.
Can we add gradient style to a Conditional Style so the colour transparency changes depending on the value?
Not currently but we plan to add this in a future release. We do have the Percent Bar that does something similar for all cells in a column.
Can we add a style that is always applied, i.e. is not based on a condition?
Yes - this is done through the Format Column function. Format Column uses the same style as a Style Condition but without an accompanying rule (e.g. if a user wants a particular column always to have a certain back colour).