Here is a leaning materials to learn Saas: a CSS preprocessor for decreasing routine operations

Skills tree Sass: CSS preprocessor

Sass syntax

Documentation Sass: Syntax

Guide Sass: Sass Basics

Article Sass - Syntax - Tutorialspoint

• How Sass parses a Stylesheet

Documentation Sass: Parsing a Stylesheet

• Sass: Structure of a Stylesheet

Documentation Sass: Structure of a Stylesheet

• Sass: writing comments

Documentation Sass: Comments

• Sass: Special Functions

Documentation Sass: Special Functions

Sass: style rules

Documentation Sass: Style Rules

Guide Sass Style Guide

• Sass: Property Declarations

Documentation Sass: Property Declarations

• Sass: Parent Selector

Documentation Sass: Parent Selector

• Sass: Placeholder Selectors

Documentation Sass: Placeholder Selectors

• Sass: Variables

Documentation Sass: Variables

Saas: At-rules

Documentation Sass: At-Rules

• Saas: @use

Documentation Sass: @use

• Saas: @forward

Documentation Sass: @forward

• Saas: @import

Documentation Sass: @import

• Saas: @mixin

Documentation Sass: @mixin and @include

• Saas: @function

Documentation Sass: @function

• Saas: @extend

Documentation Sass: @extend

• Saas: @error

Documentation Sass: @error

• Saas: @warn

Documentation Sass: @warn

• Saas: @debug

Documentation Sass: @debug

• Saas: @at-root

Documentation Sass: @at-root

• Saas: Flow Control Rules

Documentation Sass: Flow Control Rules

Tutorial Sass - Control Directives & Expressions - Tutorialspoint

Saas: values

Article Sass Variables

• Saas: numbers
• Saas: strings
• Saas: colors

-- Article SCSS Color Variables

• Saas: Lists
• Saas: maps
• Saas: booleans
• Saas: null
• Saas: functions

Saas: operators

Documentation Sass: Operators

• Saas: Equality Operators

Documentation Sass: Equality Operators

• Saas: Relational Operators

Documentation Sass: Relational Operators

• Saas: Numeric Operators

Documentation Sass: Numeric Operators

• Saas: String Operators

Documentation Sass: String Operators

• Saas: Boolean Operators

Documentation Sass: Boolean Operators

Saas: Built-In Modules

Documentation Sass: Built-In Modules

• Saas build-in modules: sass:color

Documentation Sass: sass:color

• Saas build-in modules: sass:list

Documentation Sass: sass:list

• Saas build-in modules: saas:map

Documentation Sass: sass:map

• Saas build-in modules: saas:math

Documentation Sass: sass:math

• Saas build-in modules: saas:meta

Documentation Sass: sass:meta

• Saas build-in modules: saas:selector

Documentation Sass: sass:selector

• Saas build-in modules: saas:string

Documentation Sass: sass:string

Saas: Javascript API

Documentation Sass: JavaScript API