Allow further customization of widgets

[edfloreshz]

This issue intends to report blockers encountered while trying to style libcosmic widgets.

[edfloreshz]

Checkbox

Problem

There's no support for partial check-mark status, we can either mark it as checked or not:

Having partially checked boxes is not possible yet:

Solution

Allow checkboxes to be grouped and linked to a parent checkbox, when at least one of the children is not checked, the parent checkbox will be in a partial state and will use the partial check icon.

[edfloreshz]

Radio Button

Problem

The API doesn't currently allow setting the dot size, it is not possible either to set the border to appear only when the radio button is in focus.

Solution

Add a new property to the Appearance struct and update the widget accordingly.

pub struct Appearance {
    pub background: Background,
    pub dot_color: Color,
    pub dot_size: f32,
    pub border_width: f32,
    pub border_color: Color,
    pub text_color: Option<Color>,
}

[edfloreshz]

Focus

Problem

Not all elements support the focused state.

Solution

Allow widgets to have a different style when the focused state is triggered.