tutorials/css - the complete guide/8. sizes_and_units.md

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Dimensions, Sizes And Units

Where Unit Matters

Pixels, Percentages & More

Units Sign
pixels px
percentages %
root em rem
em em
viewport height vh
viewport width vw

Some questions?

Which properties can you use in connection with these units? How is the size calculated? What's the right unit to choose?

Where Units Matter

Keeping the CSS box model in mind, going inside out, e.g from content to padding to border to margin. Lets see where we can apply these units.

font-size, padding, border, margin, width, height, top, bottom, left, right.

An Overview Of Available Sizes And Units

How is the Size Calculated?

Absolute Lengths Viewport Lengths Font-Relative Lengths
Mostly ignore user settings Adjust to current viewport Adjust to default font size
px vh rem
cm vw
mm vmin
... vmax

Also, percentage % is another special unit used.

How is the Box Size for % Units Calculated?

To understand how % units are calculated, we first need to understand the concept of containing blocks.

Rules to Remember Fixed Positioning & %