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.

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.

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.

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.

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 @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.

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.

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.

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.

The default value for animation-timing-function is ease. This timing function provides a smooth and gradual acceleration at the beginning and a deceleration at the end of the animation, creating a more natural and visually appealing effect.