[css] How to override the properties of a CSS class using another CSS class

I am fairly new to CSS3 and I want to be able to do the following:

When I add a class into a an element, it overrides the properties of another class used in this specific element.

Let's say that I have

<a class="left carousel-control" href="#carousel" data-slide="prev">

I want to be able to add a class called bakground-none, that will over override the default background in the class left.

Thanks!

There are different ways in which properties can be overridden. Assuming you have

.left { background: blue }

e.g. any of the following would override it:

a.background-none { background: none; }
body .background-none { background: none; }
.background-none { background: none !important; }

The first two “win” by selector specificity; the third one wins by !important, a blunt instrument.

You could also organize your style sheets so that e.g. the rule

.background-none { background: none; }

wins simply by order, i.e. by being after an otherwise equally “powerful” rule. But this imposes restrictions and requires you to be careful in any reorganization of style sheets.

These are all examples of the CSS Cascade, a crucial but widely misunderstood concept. It defines the exact rules for resolving conflicts between style sheet rules.

P.S. I used left and background-none as they were used in the question. They are examples of class names that should not be used, since they reflect specific rendering and not structural or semantic roles.

As an alternative to the important keyword, you could make the selector more specific, for example:

.left.background-none { background:none; }

(Note: no space between the class names).

In this case, the rule will apply when both .left and .background-none are listed in the class attribute (regardless of the order or proximity).

You should override by increasing Specificity of your styling. There are different ways of increasing the Specificity. Usage of !important which effects specificity, is a bad practice because it breaks natural cascading in your style sheet.

Following diagram taken from css-tricks.com will help you produce right specificity for your element based on a points structure. Whichever specificity has higher points, will win. Sounds like a game - doesn't it?

Checkout sample calculations here on css-tricks.com. This will help you understand the concept very well and it will only take 2 minutes.

If you then like to produce and/or compare different specificities by yourself, try this Specificity Calculator: https://specificity.keegan.st/ or you can just use traditional paper/pencil.

For further reading try MDN Web Docs.

All the best for not using !important.

LIFO is the way browser parses CSS properties..If you are using Sass declare a variable called as

"$header-background: red;"

use it instead of directly assigning values like red or blue. When you want to override just reassign the value to

"$header-background:blue"

then

background-color:$header-background;

it should smoothly override. Using "!important" is not always the right choice..Its just a hotfix

If you list the bakground-none class after the other classes, its properties will override those already set. There is no need to use !important here.

For example:

.red { background-color: red; }
.background-none { background: none; }

and

<a class="red background-none" href="#carousel">...</a>

The link will not have a red background. Please note that this only overrides properties that have a selector that is less or equally specific.

Just use !important it will help to override

background:none !important;

Although it is said to be a bad practice, !important can be useful for utility classes, you just need to use it responsibly, check this: When Using important is the right choice