PostCSS is a versatile tool that allows developers to create custom transformations or plugins for their projects. These transformations can be used to modify or extend the functionality of CSS, making it a powerful and flexible tool for developers.

The @font-face rule in CSS allows web designers to use fonts that are not installed on the user's machine. This is useful for ensuring consistent typography across different devices.

The CSS unit 'vh' represents a percentage of the viewport's height. This means that 1vh is equal to 1% of the height of the viewport in which the web page is displayed. It's a relative unit often used for responsive design.

The animation-timing-function property is used to control the speed curve of an animation. It allows you to specify how the animation progresses through time, giving you control over the easing and acceleration of the animation.

In CSS transitions, the transition-timing-function property controls the timing function for the transition. The ease-in-out option creates a smooth transition that starts slowly, accelerates in the middle, and slows down at the end. This is a common choice for animations that feel natural and pleasing to the eye.

To control how web fonts are displayed during the load process, you can adjust the font-display property in CSS. This property allows you to specify how the browser should handle font loading and rendering, with options like auto, swap, block, fallback, and optional. It helps you optimize the user experience when web fonts are slow to load or unavailable.

The value calc() in CSS allows you to perform mathematical operations on numeric values. It is a powerful feature that enables you to calculate values for various CSS properties, making it useful for responsive design and layout.

The cubic-bezier function in CSS, used for defining custom timing functions for animations, takes in three arguments. These three arguments represent the control points of the cubic Bezier curve, allowing precise control over the animation's progress.

Styled-components is a popular CSS-in-JS library for React. It allows you to define component styles directly in your JavaScript code and can easily style components based on props, making it ideal for dynamic styling based on prop values.

The CSS property that allows you to set a graphical element to be used as a mask against another element is mask-image. This property lets you specify an image or SVG as a mask, which defines the transparency of an element based on the mask's alpha channel. It's often used for creating complex visual effects and overlays.

The default value of the flex-direction property in Flexbox is row. This means that flex items are laid out in a row, horizontally. If you want them to stack vertically, you need to set flex-direction to column.

To pass values when including a mixin in SASS/SCSS, you use the @include directive followed by the mixin name. The correct syntax is @include myMixin();. This allows you to apply the styles defined in the mixin and pass any necessary values as arguments inside the parentheses.