In our documentation we guide to use @ImportHtml in MainView for global styles as a html style module.
In the global style module you can apply themable mixins to change stylable shadow parts, etc. of the components.
In case your target is not in shadow DOM, you can set the styles in custom styles block directly, e.g.
Say you have a Label and TextField in your application
// If styles.html is in src/main/java/webapp/frontend/ path is not needed
@HtmlImport("styles.html")
public class MainLayout extends VerticalLayout implements RouterLayout {
...
Label label = new Label("Title");
label.addClassName("title-label");
add(label);
...
TextField limit = new TextField("Limit");
limit.addClassName("limit-field");
add(limit);
...
}
And in src/main/java/webapp/frontend/styles.html
<custom-style>
<style>
.title-label {
color: brown;
font-weight: bold;
}
...
</style>
</custom-style>
<dom-module theme-for="vaadin-text-field" id="limit-field">
<template>
<style>
:host(.limit-field) [part="value"]{
color:red
}
</style>
</template>
</dom-module>
And your "Title" text will have brown bold font, and the value in text field will be red, but its title un-affected.
See also: Dynamically changing font, font-size, font-color, and so on in Vaadin Flow web apps