The core Contact module provides a decent out-of-the-box contact form for our site. The core also provides configurable placeholders for fields. So, we add the placeholders for form fields to display placeholders to explain to the users why they should fill out the form:
Open up the d8dev site in your favorite browser, and click on the Structure link in the Admin toolbar. Click on Contact forms on the next page you can see Website feedback listed.
Now, click on Manage form display in the OPERATIONS column for the Website feedback form:
On the next screen, you can see that the Subject and Message fields are configurable:
Now, click on the settings icon for the Subject field, fill in Placeholder as
Please enter your subject here!, and click on the Update button:
Next, click on the settings icon for the Message field, fill in Placeholder as
Please enter your Message here!, change the Rows value from12to8, and click on the Update...