CSS Font Size
Font Size
The font-size property sets the size of the text.
Being able to manage the text size is important in web design. However, you
should not use font size adjustments to make paragraphs look like headings, or
headings look like paragraphs.
Always use the proper HTML tags, like <h1> - <h6> for headings and <p> for
paragraphs.
The font-size value can be
an absolute, or relative size.
Absolute size:
Sets the text to a specified size
Does not allow a user to change the text size in all browsers (bad for accessibility reasons)
Absolute size is useful when the physical size of the output is known
Relative size:
Sets the size relative to surrounding elements
Allows a user to change the text size in browsers
Note: If you do not specify a font size, the default size for normal text, like paragraphs, is 16px (16px=1em).
Set Font Size With Pixels
Setting the text size with pixels gives you full control over the text size:
Example
h1 { font-size: 40px;}
h2 { font-size: 30px;}
p { font-size: 14px;}
Try it Yourself »
Tip: If you use pixels, you can still use the zoom tool to resize the entire page.
Set Font Size With Em
To allow users to resize the text (in the browser menu), many
developers use em instead of pixels.
1em is equal to the current font size. The default text size in browsers is
16px. So, the default size of 1em is 16px.
The size can be calculated from pixels to em using this formula: pixels/16=em
Example
h1 { font-size: 2.5em; /* 40px/16=2.5em */}
h2 { font-size: 1.875em; /* 30px/16=1.875em */
}
p { font-size: 0.875em; /* 14px/16=0.875em */}
Try it Yourself »
In the example above, the text size in em is the same as the previous example
in pixels. However, with the em size, it is possible to adjust the text size
in all browsers.Unfortunately, there is still a problem with older versions
of Internet Explorer.
The text becomes larger than it should
when made larger, and smaller than it should when made smaller.
Use a Combination of Percent and Em
The solution that works in all browsers, is to set a default font-size in
percent for the <body> element:
Example
body { font-size: 100%;}
h1 { font-size: 2.5em;}
h2 { font-size: 1.875em;}
p { font-size: 0.875em;}
Try it Yourself »
Our code now works great! It shows the same text size in
all browsers, and allows all browsers to zoom or resize the text!
Responsive Font Size
The text size can be set with a vw unit, which means the "viewport width".
That way the text size will follow the size of the browser window:
Hello World
Resize the browser window to see how the font size scales.
Example
<h1 style="font-size:10vw">Hello World</h1>
Try it Yourself »
Viewport is the browser window size. 1vw = 1% of viewport width. If the viewport is 50cm wide, 1vw is 0.5cm.
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Reference: https://www.w3schools.com/css/css_font_size.asp