I want to package up a widget to be easily included in an arbitrary project. I don't want to require that the user link to my personally-created style sheet in their host page - I just want the css to be magically injected when they use my code.
I understand that CssResource can go some ways towards this dream, but after scouring documentation I haven't found any reference to natural type selectors. For instance, I want to style the <tr>s in my widget without having to add a class name to each one.
Is this achievable with GWT? GWT's own widgets all come pretty thoroughly styled, but it seems they've added a style class to every single element in the DOM!
You're on the right track - a CssResource or UiBinder's inline <ui:style> will achieve what you're looking for. With regards to styling elements by type instead of class it certainly can be done:
<ui:UiBinder>
<ui:style>
.myTable tr {
color: red;
}
</ui:style>
<table class="{style.myTable}">
<tr><td>A row!</td></tr>
</table>
</ui:UiBinder>
GWT, however, has a reason for preferring explicit class names over descendent selectors: if you have the above style, for example, every time the browser renders a <tr> element it has to walk up the DOM and visit all of the ancestors of that element to see if any of them have the .myTable class. If your application uses a lot of <tr> elements (<div> would be a better example here), most of which don't have a .myTable ancestor, it can cause a noticeable decrease in rendering performance.