How to Edit the Comments Background on a WordPress Blog

Go To Theme Customize

go to Appearance → Customize → Additional CSS:

Paste Code In Text Aria

#respond #commentform textarea {
background-color: #1A0000;
}
#respond #commentform .text,
#respond #commentform textarea {
color: #FFFFFF !important;
	font-size : 20px;
}


For Selected Text

::selection {
  color: black;
  background: white;
}

Note : Change Backgroud Color and Font Color With Your Choise