Variables can be defined using the var function:

var(--custom-name, value)

The variable name must begin with two dashes (–) and is case sensitive

/*-------------------------*/
/*-------------------------*/
/*----- CSS VARIABLES -----*/
/*-------------------------*/
/*------------------------*/
:root {
  --color-main1: #06c;
  --color-text1: #CCC;
}
/*Using the defines within your css:
var(--color-main1)
var(--color-text1)
*/


.my_class_name {
  background-color: var(--color-main1);
}