This git lets you grab the Computed style

Check CSS from Element.robot

*** Settings ***
Library    SeleniumLibrary

*** Keywords ***
Check CSS from element
    [Documentation]    This keyword only works with xpath and is based on [https://developer.mozilla.org/en-US/docs/Web/API/Window/getComputedStyle|getComputedStyle]
    ...    You can use this keyword as follows
    ...    | Check CSS from Element | //path/to/element | style | Expected Value |
    ...    | Check CSS from Element | //h2/div | font-size | 24px |
    [Arguments]    ${xpath}    ${CheckStyle}    ${ExpectedComputedStyle}
    ${ComputedStyle}    Execute Javascript    return document.defaultView.getComputedStyle(document.evaluate("${xpath}", document, null, XPathResult.FIRST_ORDERED_NODE_TYPE, null).singleNodeValue,null)['${CheckStyle}']
    Should Be Equal    ${ComputedStyle}    ${ExpectedComputedStyle}