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@import "stylesheets/ui_customisation.css?t=##last-changed-timestamp##";
(...)

 Note the "t=##last-changed-timestamp##" argument you need to add to the url, in order to discard the browser cached version of the css, when a new WAR is deployed (##last-changed-timestamp## will be replaced during WAR export with the last changed timestamp of the parent CSS)

4. Standard NG Client css

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