Answer:
make the element sizes a percentage
Step-by-step explanation:
Without using a framework specified for this type of thing such as Bootstrap, the best way to do this would be to make the element sizes a percentage. By making the size of everything a percentage it will automatically resize itself to take up the same percentage of the screen at all times. Even when the browser window is resized to any size that the user wants. This also applies to monitors of different sizes and mobile devices.