Angular 6 Material Table Sticky Header doesn't work

Question

I need to make the Header of the mat-table component fixed to the top, But It doesn't work.

I have Angular v6.1.7 and @angular/material v6.4.7.

I added the "sticky: true" propertie to the matHeaderRowDef as someone mentions here but it doesn't do anything :(

<tr mat-header-row *matHeaderRowDef="displayedColumns; sticky: true"></tr>

I have this example project: https://stackblitz.com/edit/angular-wem2qa

This is my imports on the TS file:

import { Component, Input, OnChanges, OnInit, SimpleChanges, ViewChild } from "@angular/core";
import { MatDialog, MatExpansionPanel, MatSnackBar, MatSort, MatTableDataSource, Sort } from "@angular/material";