Question.
No valid summary could be found in the resource ‘http://localhost:4200/assets/css/bootstrap.min的’integrity’ attribute. css’ with computed SHA-256 integrity ‘ nvT75FkXevX06WR8vlhFFP02xzhq9qFxLQOuS0LkWyQ=’This resource is blocked.

Causes.

      <!-- Bootstrap CSS -->
  <!-- <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css" integrity="sha384-WskhaSGFgHYWDcbwN70/dfYBj47jz9qbsMId/iRN3ewGhXQFZCSftd1LZCfmhktB" crossorigin="anonymous"> -->
    <!-- Bootstrap CSS -->
  <link rel="stylesheet" href="assets/css/bootstrap.min.css" integrity="sha384-WskhaSGFgHYWDcbwN70/dfYBj47jz9qbsMId/iRN3ewGhXQFZCSftd1LZCfmhktB" crossorigin="anonymous">

Remove:
integrity=”sha384-WskhaSGFgHYWDcbwN70/dfYBj47jz9qbsMId/iRN3ewGhXQFZCSftd1LZCfmhktB” crossorigin=”anonymous”
"anonymous"
A cross-domain request (that is, containing the Origin: HTTP header). But no authentication information is sent (that is, no cookies, X.509 certificates, and HTTP basic authentication information). If the server does not give the source site credentials (do not set access-control-allow-origin : HTTP header), the image will be contaminated and restricted.
The integrity </ code>
Contains inline metadata, which is the hash value of a resource file that you get with your browser, encoded in base64 so that users can verify that a retrieved resource has not been tampered with during transmission. Check Subresource Integrity for details.
Documents:
https://developer.mozilla.org/zh-CN/docs/Web/HTML/Element/link