[Unified Histogram] Fix toolbar button overflow on small screens (ela…

…stic#177114)

## Summary

This PR fixes an issue where the Unified Histogram toolbar buttons can
overflow on small screens.

Before:
<img width="423" alt="overflow"
src="https://github.com/elastic/kibana/assets/25592674/ce89d219-ea06-4486-88eb-3b502f661b41">

After:
<img width="423" alt="no_overflow"
src="https://github.com/elastic/kibana/assets/25592674/b576fe17-9cee-4f5c-9750-4d1073a0e8ce">

### Checklist

- [ ] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/packages/kbn-i18n/README.md)
- [ ]
[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials
- [ ] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [ ] [Flaky Test
Runner](https://ci-stats.kibana.dev/trigger_flaky_test_runner/1) was
used on any tests changed
- [ ] Any UI touched in this PR is usable by keyboard only (learn more
about [keyboard accessibility](https://webaim.org/techniques/keyboard/))
- [ ] Any UI touched in this PR does not create any new axe failures
(run axe in browser:
[FF](https://addons.mozilla.org/en-US/firefox/addon/axe-devtools/),
[Chrome](https://chrome.google.com/webstore/detail/axe-web-accessibility-tes/lhdoppojpmngadmnindnejefpokejbdd?hl=en-US))
- [ ] If a plugin configuration key changed, check if it needs to be
allowlisted in the cloud and added to the [docker
list](https://github.com/elastic/kibana/blob/main/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)
- [ ] This renders correctly on smaller devices using a responsive
layout. (You can test this [in your
browser](https://www.browserstack.com/guide/responsive-testing-on-local-server))
- [ ] This was checked for [cross-browser
compatibility](https://www.elastic.co/support/matrix#matrix_browsers)

### For maintainers

- [ ] This was checked for breaking API changes and was [labeled
appropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

src/plugins/unified_histogram/public/chart/toolbar_selector.tsx

@@ -110,7 +110,11 @@ export const ToolbarSelector: React.FC<ToolbarSelectorProps> = ({
       }}
       panelPaddingSize="none"
       button={
-        <EuiToolTip content={labelPopoverDisabled ? undefined : buttonLabel} delay="long">
+        <EuiToolTip
+          content={labelPopoverDisabled ? undefined : buttonLabel}
+          delay="long"
+          display="block"
+        >
           <ToolbarButton
             size="s"
             css={css`