To create a fluid typography system with specified limits and smooth scaling based on viewport width, you should use the clamp() function. The correct option is clamp(16px, (3vw + 1vh), 32px), which ensures the font size stays between 16px and 32px while smoothly scaling with viewport width changes.

To make the width of the button remain constant, regardless of its padding and border, you would use width: min-content. This value ensures that the button's width is only as wide as its content, ignoring padding and border.

To prevent a block of text from wrapping to the next line, you would set the white-space property to nowrap. This property prevents text from breaking at spaces or hyphens, keeping it on a single line.

A "FOUT" (Flash of Unstyled Text) occurs when web fonts take a bit of time to load, and during this time, the browser displays text in the default font before switching to the web font. This can be mitigated by using techniques like font preloading or font-display property in CSS.

To provide a fallback value for a CSS custom property, you can use the var() function. The first argument of var() is the custom property, and the second argument is the fallback value. If the custom property is not defined, the browser will use the fallback value. For example, --custom-property: var(--fallback, fallback-value); sets --custom-property to the value of --fallback if it exists, or "fallback-value" if --fallback is not defined.

When developing a slide-in sidebar menu or any animation, using the transform property is the most efficient choice for smooth performance. This is because the transform property can be hardware-accelerated by the browser, leading to faster and smoother animations. Using properties like margin, padding, or width for animations can cause reflows and repaints, which can be less performant.

To target an input element in CSS based on its validation state, you can use the :invalid pseudo-class. This selector matches input elements that have failed validation, such as a required field left blank or an email input with an invalid format. For example, input:invalid { border: 2px solid red; } can be used to style invalid input elements.

In CSS transitions, the "transition-delay" property is used to introduce a delay before the transition begins. This allows you to control when the transition effect starts after a triggering event, such as a hover or click.

The main advantage of using CSS-in-JS is improved code maintainability. With CSS-in-JS, styles are encapsulated within the component they belong to, reducing the chances of style conflicts and making it easier to manage and maintain styles in a complex application. It promotes a more component-oriented and self-contained approach to styling, enhancing the overall maintainability of your codebase.

To make an image slide in and stay in place after the animation finishes, you should use position: absolute to position it, left: 0 to ensure it starts from the left edge, animation-fill-mode: forwards to maintain the final state after the animation, and animation-timing-function: ease-in-out to control the animation timing for a smooth effect.