When a new page has been pushed, clicking the arrow in the toolbar does not work

I have created a tabbed application. In the home page (the first tab), I called this.navCtrl.push(SomePage);. When SomePage has been pushed, the toolbar shows a back arrow button. Pressing the system back button returns the home page, but pressing the toolbar’s arrow does nothing. What should I change?

It seems that the problem is caused by the CSS that I used to centre the title. I had set this CSS, which I got from Google search result, in the app.scss to centre the title. When I removed the CSS, the back button worked.

// .title.title-md {
// position: absolute;
// left: 0;
// top: 0;
// height: 100%;
// width: 100%;
// text-align: center;
// }

But how can I centre the title and get the back button work at the same time?