Most modern websites use responsive web design techniques to ensure they look good, are readable, and remain usable on devices with any screen size, i.e. mobile phones, tablets, laptops, desktop PC monitors, televisions, projectors, and more.
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Sites using these techniques have a single template, which modifies the layout in response to the screen dimensions:
Smaller screens typically show a linear, single-column view where UI controls such as menus are activated by clicking (hamburger) icons. Larger screens show more information, perhaps with horizontally-aligned sidebars. UI controls such as menu items may always be visible for easier access.