CSS Units Explained: When to Use px, vw, and vh in Web Design

Web developers use three common CSS units to control the size and layout of elements on a page. Pixels (px) are fixed units that remain constant regardless of screen size or browser window changes. Viewport width (vw) is a relative unit tied to the browser window's width, so 10vw on a 1200px-wide screen equals 120px but shrinks to 60px if the window narrows to 600px. Viewport height (vh) works similarly but is based on screen height, making it useful for elements like hero images that need to fill the full vertical space of any device. Choosing between these units depends on whether a design element should stay fixed or scale dynamically with the user's screen.