Add "Get CSS Property Value" keyword to retrieve computed CSS values

[b-vamsipunnam]

Summary
Adds a new keyword Get CSS Property Value to SeleniumLibrary for retrieving computed CSS property values from web elements.

Motivation
SeleniumLibrary provides keywords for accessing DOM attributes (Get DOM Attribute) and element properties (Get Property), but does not offer a direct way to retrieve computed CSS values.

Implementation

• Added Get CSS Property Value in src/SeleniumLibrary/keywords/element.py
• Supports both locator strings and WebElement inputs
• Returns browser-computed CSS values (e.g., rgba(...), px)

Tests

• Added acceptance tests in atest/acceptance/keywords/elements.robot covering:
• Multiple CSS properties (display, font-size, margin-top, text-align)
• Computed values (background-color)
• Missing element handling
• WebElement usage

Added test fixture:

• atest/resources/html/cssproperties.html

Updated unit test keyword count to 183 in:

• utest/test/api/test_plugins.py

Files Changed:

• src/SeleniumLibrary/keywords/element.py
• atest/acceptance/keywords/elements.robot
• atest/resources/html/cssproperties.html
• utest/test/api/test_plugins.py

Related Issues
No existing issue found.

Request
If this contribution aligns with project standards, I would appreciate consideration for adding the acknowledge label.

Thank you !