To use a custom property in your styles in CSS, you reference it with the @ symbol. Custom properties, also known as CSS variables, are defined using the :root pseudo-class, and their values can be accessed and used in your styles by prefixing the custom property name with the @ symbol.

The inherit value in CSS makes the element inherit the computed value of the property from its parent element. It ensures that the property's value is taken from the parent element, allowing for consistent styling throughout the document.

The @keyframes rule in CSS is used to create animations over a set duration. You define specific animation steps within the @keyframes rule, and then you can apply this animation to elements using the animation property. It allows you to control how an element changes over time.

To blend the background images of an element in CSS, you should use the background-blend-mode property. This property allows you to control how the background images blend with each other and with the element's background color. It offers various blending modes to achieve different visual effects.

The "~" (tilde) combinator in CSS is used to select elements that are siblings and share the same parent. It selects all siblings that match the specified selector.

The main advantage of using a modular CSS approach is that it simplifies CSS development by encouraging a component-based structure and the creation of reusable code. This approach makes it easier to manage and maintain styles, improves code reusability, and reduces the chances of CSS conflicts and errors.

The 'box-sizing' property with a value of 'border-box' makes the element's content box include the padding and border, ensuring that the specified width or height of the element includes everything within it, making layout and sizing more predictable and intuitive.

The CSS property used to change the text case, such as making text all uppercase, is text-transform. It allows you to control the capitalization of text, including options like uppercase, lowercase, and capitalize. This is especially useful for headings and other text elements where you want to change the case style.

The @keyframes rule in CSS is used to specify the keyframes for CSS animations. Keyframes describe how an animation progresses from the starting state to the ending state. They define the intermediate steps or percentage-based changes in the animation's properties, allowing for smooth and controlled animations.

For setting the "line-height" property to ensure consistent spacing, the recommended unit is typically "em." Using "em" units allows the line height to be relative to the font size, which ensures that the spacing remains consistent even if the text size changes. This is especially useful for creating responsive and accessible web designs.