Try using below CSS:

```
<style>
    div[class^="logoCell-"] {
       display: none !important;
    }
</style>
```
Also, if it is not working using alternate CSS then you can try adding it using **SPFx Application customizer** (if you want to hide it from all modern pages) or Modern Script Editor webpart (if you want to hide it from only one page).

**Reference**:

[Inject Custom CSS on SharePoint Modern Pages using SPFx Extensions](https://tahoeninjas.blog/2018/05/08/inject-custom-css-on-sharepoint-modern-pages-using-spfx-extensions/)