<div class="suchfeld">
  <form [formGroup]="searchForm">
    <md-input-container style="width: 120px;">
      <input mdInput type="text" placeholder="Suchbegriff" formControlName="searchTerm"
             (keyup.enter)="suche.emit(searchForm)">
    </md-input-container>
    <md-input-container style="width:50px !important; display: block;">
      <input mdInput type="number" min="1" max="300" placeholder="Seite / Blatt" formControlName="page"
             (keyup.enter)="suche.emit(searchForm)">
    </md-input-container>
  </form>
</div>

<div class="suchfeld">
  <form [formGroup]="searchForm">
    <md-input-container style="width: 120px;">
      <input mdInput type="text" placeholder="Suchbegriff" formControlName="searchTerm"
             (keyup.enter)="suche.emit(searchForm)">
    </md-input-container>
    <md-input-container style="width:75px !important; display: block;">
      <input mdInput type="number" min="1" max="300" placeholder="Seite / Blatt" formControlName="page"
             (keyup.enter)="suche.emit(searchForm)">
    </md-input-container>
  </form>
</div>

Set width of page search field to 75px
Set width of page search field to 75px
