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CSS: Variables

A modern website contains thousands of lines of styles. Styles for blocks, text, and small areas are often all in one place. Imagine this: there's a certain shade of red that we use in lots of different blocks.

How convenient would it be to change all the values if you want to change the base color? That's right - we would have to find all the values within the file and replace them with new ones.

This has been one of the main problems with CSS for a long time. With the advent of the CSS3 standard, this problem has gone thanks to variables.

Variables in programming are a small area of memory in which we store the desired value. This value can always be accessed from any available location.

As in programming, in CSS, you can specify variables that will be available throughout site development. If variables are used, you can quickly replace some values with other values instead of having to replace property values manually.

A variable is created using the --variable-name construct. You can choose the name of the variable yourself. As an example, let's create a variable called --main-color that contains the base color of the pages. Set it to be black:

--main-color: #000000;

This simplicity hides the fact that variables have different scopes, areas of the file from which they can be used. This is a big topic, so let's talk only about global scope for now. This will allow a variable to be used in any area of the CSS file.

To create a global variable, you need to specify it in a special construct, :root. This is usually done at the beginning of the CSS file:

:root {
  --main-color: #000000;

You can now use a variable in any part of our CSS code. This is done with a special construction, var(--variable-name).

:root {
  --main-color: #000000;

.news-block {
  background-color: var(--main-color);

.left-sidebar {
  background-color: var(--main-color);

If we want to set a different shade of black, just change the value of the -main-color variable, and all changes will automatically apply to blocks with the .news-block and .left-sidebar classes


Create a variable called --main-blue and set its value to the color blue #00bfff. Declare the variable in :root. Write the styles in the <style> tag

The exercise doesn't pass checking. What to do? 😶

If you've reached a deadlock it's time to ask your question in the «Discussions». How ask a question correctly:

  • Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.
In my environment the code works, but not here 🤨

Tests are designed so that they test the solution in different ways and against different data. Often the solution works with one kind of input data but doesn't work with others. Check the «Tests» tab to figure this out, you can find hints at the error output.

My code is different from the teacher's one 🤔

It's fine. 🙆 One task in programming can be solved in many different ways. If your code passed all tests, it complies with the task conditions.

In some rare cases, the solution may be adjusted to the tests, but this can be seen immediately.

I've read the lessons but nothing is clear 🙄

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