How to determine the CSS unit of a responsive website?
Hai Yong* 2021-08-09 18:57:12

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Nice to meet you again !

When we create responsive websites for a variety of devices , Know the right CSS The unit is very important . But before delving into decision-making , Let's classify them first to understand their purpose .

1. Absolute units

  • px - Pixels
  • pt - spot
  • pc - Picas
  • in - Inch
  • cm - centimeter
  • mm - mm

2. Percentage units

  • percentage % Company

3. Relative units

  • Relative to font size

    • em
    • rem - root em
  • Relative to the viewing port / file

    • vw
    • vh
    • vmax
    • vmin

Learn the most common units here

px Company

Absolute pixel units are only used on the screen ( Interface ), The remaining units are used for printing .px Unit is not a good choice , In fact, this is not for scaling . Whatever screen size you choose ,px The dimensions of the units are fixed . That's why borders are always preferred px Unit reasons , Because the border remains fixed on all screen sizes .

% Company

This is used to set the width of the element , It is always relative to the size of its immediate parent element . If there is no defined parent , By default body Be considered a parent .

Consider a width of 500px Box , There's a h1 Elements

.box{

width: 500px;
border: 1px solid crimson;
padding: 10px;
}
h1{

width: 50%;
border: 1px solid;
}

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If no parent is defined , that root Will be treated as the default parent .

em Company

em The unit is always relative to the font size of its immediate parent .1em == A parent font size . If not covered , The default font size is 16px, Suppose the font size in the parent element is 48px, Then in the child element is 1em == 48px.

h1{

font-size: 1em; /* now 1em == 16px */
}

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.container{

font-size: 48px;
/* or 3em, Because the default font size is 16px & Its parent element is body, therefore 3*16px Namely 48px */
}
h1{

font-size: 1em; /* now 1em == 48px */
}

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We can use this unit for margins and padding , Because it allows us to use flexible spacing around the box according to the font size of the element . Elements font-size It will vary according to the size of the device , Therefore, the spacing around the elements will also change separately .

rem Company

r representative root em, And em Different , It is always relative to the root font size , No matter what font size its next parent element has . If the root has redefined the font size , Such as 60px that 1rem == 60px .

html{

font-size: 60px;
}
.container{

font-size: 16px;
}
h1{

font-size: 1rem;
}

effect
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vw Company

vw representative viewprot width( Viewport width ), It means vw Always relative to the root width 1%, Independent of the width of the parent element . therefore , If 1vw == 1% that 100vw == 100% Viewport width .

Let's consider the following example , The width of one of the children is relative to the size of the parent , The width of the other subitem is relative to the root .

.container{

width: 600px;
border: 2px solid black;
text-align: center;
font-size: 20px;
}
.box1{

width: 100%;
background: skyblue;
}
.box2{

width: 70vw;
background: pink;
}

effect
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* vh Company

vh representative viewprot height ( Viewport height ), Such as vw It's also relative to the root / Document 1% Height . Let's consider the following example , The height of one of the children is related to the size of the parent , The height of another child is related to the root .

.container{

border: 2px solid;
font-size: 40px;
width: 800px;
height: 400px;
display: flex;
text-align: center;
margin: 0 auto;
}
.box1{

height: 100%;
width: 50%;
background: skyblue;
}
.box2{

height: 100vh;
background: pink;
width: 50%;
}

effect
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wuhu ! take off !

Summarize

px Units are often used for borders .
% The width of the unit relative to the parent .
em The margin and padding of the unit relative to the font size of the element .
rem The font size of the unit relative to the root .
vw and vh Represents the width and height relative to the root .
These are 6 individual css unit , They are most commonly used to make websites responsive .

I've been writing a technology blog for a long time , And mainly through CSDN publish , This is my article Of responsive websites CSS Unit tutorial . I like to share technology and happiness through articles . You can visit my blog : https://haiyong.blog.csdn.net/ To learn more . I hope you will like !

You are welcome to put forward your opinions and suggestions in the comment area !

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