<form *ngIf="filtersForm" [formGroup]="filtersForm" fxLayout="row" fxLayout.lt-sm="column" fxLayoutGap="2.5em" fxLayoutGap.xs="0">
  <mat-form-field fxFlex="100" fxHide.gt-xs>
    <mat-select formControlName="categoryId" placeholder="Category">
      <mat-option *ngFor="let category of optionsService.categoryOptions" [value]="category.id">
        {{category.name}}
      </mat-option>
    </mat-select>
  </mat-form-field>

  <div fxFlex="50">
    <div fxLayout="column">
      <app-mat-tags style="display: block;" fxFlex="100" *ngIf="showPersonFilter" [placeholder]="'People'"
                    [addNew]="false" [source]="personTagSource" formControlName="personTags"></app-mat-tags>
      <app-mat-tags style="display: block;" fxFlex="100" *ngIf="showOrgUnitFilter" [placeholder]="'Organisation units'"
                    [addNew]="false" [source]="orgUnitTagSource" formControlName="orgUnitTags"></app-mat-tags>
    </div>
  </div>

  <div fxLayout="column" fxFlex="50">
    <app-research-activity-input style="display: block;" *ngIf="showResearchActivityFilter"
                                 formControlName="researchActivityIds"></app-research-activity-input>
  </div>
</form>

<form *ngIf="filtersForm" [formGroup]="filtersForm"  fxLayout="row" fxLayout.lt-sm="column" fxLayoutGap="2.5em" fxLayoutGap.xs="1em">
  <div fxHide.gt-xs>
    <mat-form-field fxFlex="100" style="margin-top: 1em !important;">
      <mat-select formControlName="categoryId" placeholder="Category">
        <mat-option *ngFor="let category of optionsService.categoryOptions" [value]="category.id">
          {{category.name}}
        </mat-option>
      </mat-select>
    </mat-form-field>
  </div>

  <div fxFlex="50">
    <div fxLayout="column" fxLayoutGap="1em">
      <app-mat-tags style="display: block;" fxFlex="100" *ngIf="showPersonFilter" [placeholder]="'People'"
                    [addNew]="false" [source]="personTagSource" formControlName="personTags"></app-mat-tags>
      <app-mat-tags style="display: block;" fxFlex="100" *ngIf="showOrgUnitFilter" [placeholder]="'Organisation units'"
                    [addNew]="false" [source]="orgUnitTagSource" formControlName="orgUnitTags"></app-mat-tags>
    </div>
  </div>

  <div fxLayout="column" fxFlex="50">
    <app-research-activity-input style="display: block;" *ngIf="showResearchActivityFilter"
                                 formControlName="researchActivityIds"></app-research-activity-input>
  </div>
</form>

Add more white space to form fields
Add more white space to form fields
