Conditional css, display message in table cell for current date<start date

Question

this is my table in html file

     <table
        mat-table
        [dataSource]="dataSource"
      >
  
        <!-- Start Date Column -->
        <ng-container matColumnDef="startDate">
          <th
            mat-header-cell
            *matHeaderCellDef
       
            style="width: 25%"
          >
            Start Date
          </th>
          <td
            mat-cell
            class="info_data_size"
            *matCellDef="let element
      title="date is less""error"
          >
            {{startDate}}
          </td>
        </ng-container>
    ...

if the start date in a table column is less than current date, then a message should be displayed saying "date is less" how do I put condition on the title similar to Add hover text without javascript like we hover on a user's reputation but for individual table cells