What is the width of any div elements on a 750px screen given the following CSS rules: div { width: 80%; } @media all and (min-width: 500px) { div { width: 25%; } }?

The correct choice is based on understanding how CSS rules apply under different conditions, especially when media queries are involved. In this scenario, the CSS specifies that by default, all <div> elements should have a width of 80%. However, there is a media query that modifies this width for screens that have a minimum width of 500px, changing it to 25%.

Since a 750px screen meets the condition established by the media query (it's wider than 500px), the browser applies the specific rule within the media query. Therefore, the width of the <div> elements on a 750px screen will be set to 25%.

In contrast, if the media query had not been applicable or if the screen size had been below 500px, the default rule of 80% would remain effective. Thus, recognizing the role of media queries in CSS is crucial for determining how styles adapt to varying screen sizes.