[Bug] useless css Or is the class name browser-chrome missing in the html?

Nobody has claimed this yet.

### What is this about?

The code in the `ui/css/itcss/components/newui-sections.scss` for fixing UI lag on external monitor is still existing.
The target html DOM is missing the browser.
Is this css style still needed or is the DOM missing the class name?

```
.app.os-mac.browser-chrome::after {
content: "";
position: fixed;
top: 0;
left: 0;
width: 1px;
height: 1px;
background-color: var(--color-background-alternative);
animation: emptySpinningDiv 1s infinite linear;
}

@keyframes emptySpinningDiv {
0% { transform: rotate(0deg); }
to { transform: rotate(1turn); }
}

// Main container
.main-container {
display: flex;
flex-direction: column;
z-index: design-system.$main-container-z-index;
}
```

## Reference
https://github.com/MetaMask/metamask-extension/issues/10173
https://github.com/MetaMask/metamask-extension/pull/10952

### Scenario

_No response_

### Design

_No response_

### Technical Details

_No response_

### Threat Modeling Framework

_No response_

### Acceptance Criteria

_No response_

### Stakeholder review needed before the work gets merged

- [ ] Engineering (needed in most cases)
- [ ] Design
- [ ] Product
- [ ] QA (automation tests are required to pass before merging PRs but not all changes are covered by automation tests - please review if QA is needed beyond automation tests)
- [ ] Security
- [ ] Legal
- [ ] Marketing
- [ ] Management (please specify)
- [ ] Other (please specify)

### References

_No response_

Start with ui/css/itcss/components/newui-sections.scss and inspect the current HTML class assignment for the app, operating system, and browser. Compare the behavior and rationale with issues #10173 and pull request #10952. Done means determining whether the rule is obsolete or the browser-chrome class is missing, then documenting or correcting that state.

Written by the indexing model from the issue text.