HI 
Navigate to Service Portal > Portals.
Select the Portal that you are using. If it's the Employee center, then Employee center, esc (URL Suffix).

Now., open the Theme record

Make sure you are in Employee center Application.

After opening the theme record, Create New Record.

Now, Name = Mandatory field color and from the Style Sheet create new record by clicking on the  Reference record.

Give a Name - Mandatory field color Mandatory
CSS:

.v3c29786e87133200e0ef0cf888cb0bdf .sc-field-error-label {
    
    background-color: #ffffff !important;
    
}

Click Submit.

Now Submit the CSS Include.

Now, Make sure the file is added in the CSS Includes.

To conclude, I am just overriding the color of the fields color.

If the above information helps you, Kindly mark it as Helpful and Accept the solution.


Regards,
Najmuddin.