Css var in calc

Creating Responsive Designs with CSS Calc() and CSS Variables

Creating responsive designs has become an essential aspect of modern web development. With the diverse range of devices available today, it’s crucial to ensure that your website looks and functions well on all screen sizes. In this blog post, we will explore the power of CSS calc() function and CSS Variables (also known as Custom Properties) to create flexible and maintainable responsive designs. By the end of this post, you will have a deeper understanding of these powerful tools and how to use them effectively in your projects.

Introduction to CSS Calc() Function

The calc() function is a powerful CSS feature that allows you to perform calculations with numbers and units, resulting in a computed value. This function can be used in any CSS property that accepts numerical values, such as width, height, padding, margin, and so on. It’s an excellent tool for creating responsive designs, as it enables you to mix different units, such as pixels, percentages, and viewport units, to create flexible sizing and positioning.

Syntax of Calc()

The calc() function follows a simple syntax:

The expression inside the parentheses can contain addition, subtraction, multiplication, or division operations. The operands must be valid CSS values, such as lengths, angles, or time. Here’s a simple example:

/* Using calc() to calculate the width of an element */ .width-example  width: calc(50% - 20px); >

In this example, the width of the element is calculated by subtracting 20 pixels from 50% of the container’s width.

Introduction to CSS Variables

CSS Variables, also known as Custom Properties, are a powerful feature that allows you to define and reuse values throughout your stylesheets. This makes it easy to maintain and update your styles, as you can change a single value, and all the instances of that variable will be updated automatically.

Defining and Using CSS Variables

To define a CSS variable, you use the following syntax:

element  --variable-name: value; >

The variable name must start with two hyphens ( — ), followed by a valid custom property name, which can consist of letters, digits, hyphens, and underscores. To use a CSS variable, you refer to it with the var() function:

element  property: var(--variable-name); >

Here’s a simple example of defining and using a CSS variable:

:root  --main-color: #f06; > .header  background-color: var(--main-color); >

In this example, the —main-color variable is defined at the :root level, which makes it globally available throughout the stylesheet. The header element then uses the —main-color variable to set its background color.

Creating Responsive Designs with CSS Calc() and CSS Variables

Now that we have a basic understanding of the CSS calc() function and CSS variables, let’s see how we can combine these powerful features to create responsive designs.

Flexible Grid Layout

Let’s create a flexible grid layout using CSS calc() and CSS variables. We’ll start by defining some basic variables:

:root  --gutter: 10px; --columns: 4; >

Here, we define the gutter size (the space between grid items) and the number of columns in our grid.

Next, we’ll create a simple grid container and grid items:

div class="grid-container"> div class="grid-item">Item 1div> div class="grid-item">Item 2div> div class="grid-item">Item 3div> div class="grid-item">Item 4div> div>

Now, let’s style our grid container and grid items using CSS calc() and CSS variables:

.grid-container  display: flex; flex-wrap: wrap; margin-left: calc(var(--gutter) * -1); margin-right: calc(var(--gutter) * -1); > .grid-item  flex: 0 0 calc(100% / var(--columns) - var(--gutter) * 2); margin: var(--gutter); box-sizing: border-box; >

In this example, we use the calc() function to calculate the width of each grid item based on the number of columns and the gutter size. We also set negative margins on the grid container to counteract the gutter size, ensuring that the grid items align with the container edges.

Responsive Typography

Another use case for CSS calc() and CSS variables is to create responsive typography. Let’s define some variables for font sizes and breakpoints:

:root  --font-size-base: 16px; --font-size-lg: 24px; --breakpoint-md: 768px; --breakpoint-lg: 1024px; >

Now, let’s create a responsive typography style using these variables:

body  font-size: calc(var(--font-size-base) + (var(--font-size-lg) - var(--font-size-base)) * (100vw - 320px) / (var(--breakpoint-md) - 320)); > @media (min-width: calc(var(--breakpoint-md) + 1px))  body  font-size: var(--font-size-lg); > >

In this example, we use the calc() function to create a fluid font size that grows linearly between —font-size-base and —font-size-lg as the viewport width increases from 320px to —breakpoint-md . Once the viewport width exceeds —breakpoint-md , the font size is fixed at —font-size-lg .

FAQ

Q: Can I use CSS calc() with CSS variables in older browsers?

A: The support for CSS calc() and CSS variables is quite good in modern browsers. However, older browsers, such as Internet Explorer, may not support these features. You can use tools like Autoprefixer to generate fallbacks for older browsers, or consider using polyfills like postcss-custom-properties and calc-polyfill for better compatibility.

Q: Are there any performance concerns when using CSS calc() and CSS variables?

A: Generally, the performance impact of using CSS calc() and CSS variables is negligible. However, it’s essential to avoid using overly complex expressions or using these features in places where they might cause unnecessary reflows or repaints. As always, it’s best to test your website’s performance and optimize as needed.

Q: Can I use CSS calc() with CSS variables in CSS animations and transitions?

A: Yes, you can use CSS calc() and CSS variables in animations and transitions. However, keep in mind that not all properties can be animated or transitioned, and some complex expressions might cause performance issues.

Q: How can I debug CSS calc() and CSS variable issues?

A: Debugging CSS calc() and CSS variable issues can be done using browser developer tools. You can inspect computed styles to see how the browser interprets your calc()expressions and CSS variables. Additionally, you can use the browser’s console to log and evaluate specific expressions or variables if needed. It’s essential to verify that your expressions are valid and that the variables are correctly defined and used.

Conclusion

In this blog post, we explored the power of CSS calc() function and CSS Variables to create flexible, maintainable, and responsive designs. By combining these features, we can build complex layouts and typography that adapt to different screen sizes and resolutions, improving the overall user experience.

Remember to keep your calc() expressions as simple as possible and use CSS variables wisely to ensure maintainability and performance. With the proper understanding and application of these powerful tools, you can create amazing, responsive designs that look great on any device.

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calc()

The calc() CSS function lets you perform calculations when specifying CSS property values. It can be used with , , , , , , or values.

Try it

Syntax

/* property: calc(expression) */ width: calc(100% - 80px); 

The calc() function takes a single expression as its parameter, with the expression’s result used as the value. The expression can be any simple expression combining the following operators, using standard operator precedence rules:

Multiplication. At least one of the arguments must be a .

Division. The right-hand side must be a .

Notes

Serializing the arguments inside calc() follows the IEEE-754 standard for floating point math which means there’s a few cases to be aware of regarding the infinity and NaN constants. For more details on how constants are serialized, see the calc-constant page.

In addition, the following notes apply:

• The + and — operators must be surrounded by whitespace. For instance, calc(50% -8px) will be parsed as «a percentage followed by a negative length» — which is an invalid expression — while calc(50% — 8px) is «a percentage followed by a subtraction operator and a length». Likewise, calc(8px + -50%) is treated as «a length followed by an addition operator and a negative percentage».
• The * and / operators do not require whitespace, but adding it for consistency is recommended.
• Math expressions involving percentages for widths and heights on table columns, table column groups, table rows, table row groups, and table cells in both auto and fixed layout tables may be treated as if auto had been specified.
• It is permitted to nest calc() functions, in which case the inner ones are treated as simple parentheses.
• For lengths, you can’t use 0 to mean 0px (or another length unit); instead, you must use the version with the unit: margin-top: calc(0px + 20px); is valid, while margin-top: calc(0 + 20px); is invalid.
• The calc() function cannot directly substitute the numeric value for percentage types; for instance calc(100 / 4)% is invalid, while calc(100% / 4) is valid.

Formal syntax

=
calc( )

=
[ [ ‘+’ | ‘-‘ ] ]*

=
[ [ ‘*’ | ‘/’ ] ]*

=
|
|
|
|
( )

=
e |
pi |
infinity |
-infinity |
NaN

Accessibility concerns

When calc() is used for controlling text size, be sure that one of the values includes a relative length unit, for example:

h1  font-size: calc(1.5rem + 3vw); > 

This ensures that text size will scale if the page is zoomed.

Usage with integers

This will give .modal a final z-index value of 2.

Examples

Positioning an object on screen with a margin

calc() makes it easy to position an object with a set margin. In this example, the CSS creates a banner that stretches across the window, with a 40-pixel gap between both sides of the banner and the edges of the window:

.banner  position: absolute; left: 40px; width: calc(100% - 80px); border: solid black 1px; box-shadow: 1px 2px; background-color: yellow; padding: 6px; text-align: center; box-sizing: border-box; > 

div class="banner">This is a banner!div> 

Automatically sizing form fields to fit their container

Another use case for calc() is to help ensure that form fields fit in the available space, without extruding past the edge of their container, while maintaining an appropriate margin.

input  padding: 2px; display: block; width: calc(100% - 1em); > #form-box  width: calc(100% / 6); border: 1px solid black; padding: 4px; > 

Here, the form itself is established to use 1/6 of the available window width. Then, to ensure that input fields retain an appropriate size, we use calc() again to establish that they should be the width of their container minus 1em. Then, the following HTML makes use of this CSS:

form> div id="form-box"> label for="misc">Type something:label> input type="text" id="misc" name="misc" /> div> form> 

Nested calc() with CSS Variables

You can also use calc() with CSS variables. Consider the following code:

.foo  --widthA: 100px; --widthB: calc(var(--widthA) / 2); --widthC: calc(var(--widthB) / 2); width: var(--widthC); > 

After all variables are expanded, widthC ‘s value will be calc(calc(100px / 2) / 2) , then when it’s assigned to .foo ‘s width property, all inner calc() s (no matter how deeply nested) will be flattened to just parentheses, so the width property’s value will be eventually calc((100px / 2) / 2) , i.e. 25px . In short: a calc() inside of a calc() is identical to just parentheses.

Specifications

Browser compatibility

BCD tables only load in the browser

See also

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This page was last modified on Jul 18, 2023 by MDN contributors.

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