Touchkit ignores the @Theme setting and always forces the touchkit theme

[vaadin-bot]

Originally by mvysny2

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I have @theme("mytheme") attached to my UI; yet Touchkit completely ignores my custom styles.css file with just a simple content:
.v-label-label-ellipsize {
background: blue !important;
}

If I forcibly add the theme with
getPage().getStyles().add(".v-label-label-ellipsize { background: blue !important; }");
It starts to work.
I have tried getPage().getStyles().add(new ThemeResource("styles.css"));
and here is the source of the problem: this gets added to the html's head section:

So it is clear that Touchkit ignores the @theme setting and always use the touchkit theme.
I tried a workaround which worked: getPage().getStyles().add(new ClassResource("styles.css"));
I'm using Touchkit 4.0.4

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Imported from https://dev.vaadin.com/ issue #19369