What is the correct way to define a variable in SASS? code example

Example 1: scss variables

$base-color: #c6538c;

Example 2: scss variables

$base-color: #c6538c;
$border-dark: rgba($base-color, 0.88);

.alert {
  border: 1px solid $border-dark;
}

Example 3: variables scss

// SCSS variables

$darkcolor: #605C4D;
$large: 350px;

section{
	background-color: $darkcolor;
  	height: $large;
}

Example 4: Sass Variables

$myFont: Helvetica, sans-serif;
$myColor: red;
$myFontSize: 18px;
$myWidth: 680px;

body {
  font-family: $myFont;
  font-size: $myFontSize;
  color: $myColor;
}

#container {
  width: $myWidth;
}

Example 5: how to make a scss variable

$variableName = item

$gray = #404040

body{
	background:$gray; 
}