[8.18] Fix vega tooltip color in dark mode (#212042) (#213083)

# Backport

This will backport the following commits from `main` to `8.18`:
- [Fix vega tooltip color in dark mode
(#212042)](#212042)

<!--- Backport version: 9.6.6 -->

### Questions ?
Please refer to the [Backport tool
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<!--BACKPORT [{"author":{"name":"Marco
Vettorello","email":"marco.vettorello@elastic.co"},"sourceCommit":{"committedDate":"2025-03-04T12:07:52Z","message":"Fix
vega tooltip color in dark mode (#212042)\n\n## Summary\n\nThis PR fixes
the text color of the vega tooltip.\nThe Vega tooltip is always dark
because uses the euiTooltip style for\nit. There was the `lightShade`
color used within this tooltip before\nthat result in an invisible text
color when running in dark mode.\nThe PR removes the custom colors and
makes the tooltip inherits the\ncolors from the euiTooltip
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vega tooltip color in dark
mode","number":212042,"url":"https://github.com/elastic/kibana/pull/212042","mergeCommit":{"message":"Fix
vega tooltip color in dark mode (#212042)\n\n## Summary\n\nThis PR fixes
the text color of the vega tooltip.\nThe Vega tooltip is always dark
because uses the euiTooltip style for\nit. There was the `lightShade`
color used within this tooltip before\nthat result in an invisible text
color when running in dark mode.\nThe PR removes the custom colors and
makes the tooltip inherits the\ncolors from the euiTooltip
style.","sha":"4b4c15a943dbe114cda3da8b99208f29549efbbd"}},"sourceBranch":"main","suggestedTargetBranches":[],"targetPullRequestStates":[{"branch":"main","label":"v9.1.0","branchLabelMappingKey":"^v9.1.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/212042","number":212042,"mergeCommit":{"message":"Fix
vega tooltip color in dark mode (#212042)\n\n## Summary\n\nThis PR fixes
the text color of the vega tooltip.\nThe Vega tooltip is always dark
because uses the euiTooltip style for\nit. There was the `lightShade`
color used within this tooltip before\nthat result in an invisible text
color when running in dark mode.\nThe PR removes the custom colors and
makes the tooltip inherits the\ncolors from the euiTooltip
style.","sha":"4b4c15a943dbe114cda3da8b99208f29549efbbd"}}]}]
BACKPORT-->

Co-authored-by: Marco Vettorello <marco.vettorello@elastic.co>

src/platform/plugins/private/vis_types/vega/public/vega_view/vega_tooltip.styles.ts

@@ -53,7 +53,6 @@ export const vegaVisTooltipStyles = (euiThemeContext: UseEuiTheme) => {
             'max-width',
             mathWithUnits(euiTheme.size.base, (x) => x * 10)
           )}
-          color: ${euiTheme.colors.lightShade};
           ${logicalTextAlignCSS('right')}
           ${logicalCSS('padding-right', euiTheme.size.xs)}
         }