Angular Material is one of the most favoured User Interfaces for Angular Web Application development. Angular Material is known for its easy binding with Angular Code and web applications built using Angular alongside Angular Material performs better when compared to other UI frameworks.

Although Angular Material has good performance, it is still known for its bugs and glitches when it comes to the user interface. Recently, the current version of Angular Material has this glitch in the coding especially when users incorporate the darker theme especially, pink-bluegrey.css theme. The main glitch which is noted is that, when a mat-input is incorporated, the field border and the text cursor is not visible. When we look into it, we find that it's not a bug but a glitch which has to be fixed manually. This can be fixed by simply adding a dark background colour to the division or container which holds the mat input field.

In order to insert the input field, import MatImportModule in app.module.ts first. Later from the documentation site of Angular Material copy and paste the example mat form field. Be cautious to copy-paste the HTML, CSS elements in the respective component. 

@import "~@angular/material/prebuilt-themes/indigo-pink.css";
<form class="example-form">
  <mat-form-field class="example-full-width">
    <input matInput placeholder="Favorite food" value="Sushi">
  </mat-form-field>

  <mat-form-field class="example-full-width">
    <textarea matInput placeholder="Leave a comment"></textarea>
  </mat-form-field>
</form>
.example-form {
    min-width: 150px;
    max-width: 500px;
    width: 100%; 
  }
  
  .example-full-width {
    width: 100%;
  }


By default the theme is indigo-pink and without any glitch, the browser will render the output and form fields will be visible. Now, when you change the theme to pink-bluegrey.css or purple-green.css the form input will not be visible. Following screenshot shows how it is affected. 
In order to fix this glitch, we can simply add the background colour to the form tag which contains the form input. The following coding and screenshot will show the rectified output. In the example-form CSS, add the last three classes to get the desired visible form field output.
 

.example-form {
    min-width: 150px;
    max-width: 500px;
    width: 100%; 
    background-color: black;
    color: white;
    padding: 15px
  }

Get full Source Code of MatInput Fix for Dark Theme from Github
https://github.com/rdineshkumar88/angular-material/tree/master/MatInput-Dark-Theme-Glitch-Fix