How to test expansion-panel in protractor

I am trying to test e.g. this site in protractor:
http://ift.tt/2AWat6l

I want to click on the Panel1 and expand it.

Here is my code:

it('blabla', function() {
    browser.get('http://ift.tt/2AWat6l');
    browser.sleep(10000);
    element(by.css('.mat-expansion-panel-header.ng-tns-c2-1.ng-trigger.ng-trigger-expansionHeight')).click();
    browser.sleep(1000);
});