What does _ngcontent-c# mean in Angular?

_ngcontent-c# attributes are added when you use ViewEncapsulation.Emulated – which is default. Angular uses these attributes to target specific elements with the styles. The number c is sort of a unique identifier of the host component. For example, if you have two components with the following templates:

ComponentA
<span></span>
<comp-b></comp-b>

ComponenB
<h1></h1>

Angular will mark all elements with styles inside component A as _ngcontent-c0 and all elements with styles inside component B with _ngcontent-c1:

<comp-a>
    <span _ngcontent-c0></span>
    <comp-b _ngcontent-c0>
        <h1 _ngcontent-c1></h1>
    </comp-b>
</comp-a>