How to remove space bottom mat-form-field

You can add this in your css

::ng-deep .mat-form-field-wrapper{
   margin-bottom: -1.25em;
}

NOTE: As you remove the space you cannot put <mat-hint>hint</mat-hint> or <mat-error>error</mat-error> properly.
Error and hint get inside the form-field.

Without using ::ng-deep( for Angular 8 )

Turn off encapsulation of your component inside which you change the padding.

You can do this by

import {Component,ViewEncapsulation} from '@angular/core';
@Component({
  selector: 'example',
  templateUrl: 'example.component.html',
  styleUrls: ['example.component.css'],
  encapsulation : ViewEncapsulation.None,
})
export class ExampleComponent {}

Wrap the component you want to style in a custom class. So it wont affect any other mat-form-field components.
Let’s wrap this with with my-form-field class for now

<mat-form-field class="my-form-field">
  <input matInput placeholder="Input">
</mat-form-field>

.my-form-field .mat-form-field-wrapper {
      margin-bottom: -1.25em;
}

You can add these css in global stylesheet without turning off view encapsulation. But the more elegant method is the above one.