Override Current Website CSS with a New File Without Source Access

Introduction

Customizing the appearance of a website without modifying its source code can be challenging. This question explores how to achieve this by creating a new CSS file that overrides the existing ones on a website inaccessible at the source level.

Concept of CSS Specificity

To understand how to override existing CSS, it's essential to grasp the concept of CSS specificity. It determines which CSS declarations apply to an element based on the selectors used in the rules. Specificity is calculated as follows:

• Inline: 1 | 0 | 0 | 0
• ID: 0 | 1 | 0 | 0
• Class: 0 | 0 | 1 | 0
• Element: 0 | 0 | 0 | 1

Overriding Current CSS with New CSS File

To override the existing CSS files, consider the following approach:

1. Inline Styles (Specificity: 1 | 0 | 0 | 0): Inline styles added directly to an HTML element have the highest specificity. However, they are not recommended for website-wide overrides due to their limited applicability.
2. ID Selectors (Specificity: 0 | 1 | 0 | 0): ID selectors have higher specificity than class or element selectors. Use them for unique elements that need to be styled differently within a specific context.
3. Class Selectors (Specificity: 0 | 0 | 1 | 0): Class selectors are also recommended for overriding existing styles. By assigning a specific class to an element and using a class selector in the new CSS file, you can override the styling applied by the existing CSS files.
4. Element Selectors (Specificity: 0 | 0 | 0 | 1): Element selectors have the lowest specificity. They should be used sparingly for overriding existing styles and only when more specific selectors cannot be applied.
5. !important Declaration: Using the !important declaration forces the browser to apply the specified style, regardless of its specificity. However, it should be used cautiously as it can result in unintended consequences and make it challenging to maintain consistency across styles.

Example

Consider the following HTML and CSS:

<code class="html"><article>
  <div id="id">
    <div class="class">
      <section>
        <div class="inline" style="background-color:red">
        </div>
      </section>
    </div>
  </div>
</article></code>

<code class="css">body {margin: 0;padding: 0}
div,article {min-height: 200px;height: 100%;width: 100%}

#id {
  background-color: green
}

.class {
  background-color: yellow 
}

section {
  background-color: blue 
}

.inline {
  background-color: purple !IMPORTANT /*going to be purple - final result */ 
}</code>

By using class selectors and leveraging the concept of specificity, we can effectively override the existing CSS styles and customize the appearance of the webpage according to the styles defined in the new CSS file.

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