Toolbars can be stacked up vertically in `<ion-header>`,
`<ion-content>`, and `<ion-footer>` elements. However, toolbars also
come with borders on both the top and bottom of the toolbar. To give
developers full control of the design, Ionic also includes the
`no-border-bottom` and `no-border-top` attributes. For example,
sometimes two vertically stacked toolbars may have different background
colors, in this case it might be best to leave a border between them.
However, if they have the same background color, the app may look best
without a border between them. The main point here is, it's entirely up
to the app's design to decide when and when not to show borders between
toolbars, and to do so then each toolbar can individually set
`no-border-bottom` and `no-border-top` attributes.
