The only way to edit css right now is to inject css (see https://www.sharepointdiary.com/2020/09/sharepoint-online-inject-custom-css-to-modern-sites.html)
You can download https://github.com/hugoabernier/react-application-injectcss and upload it to your tenant's App catalog.
Note: this will change the width of columns on all tables across your SharePoint sites if you were to use the example below to edit the table element:
table {
table-layout: fixed;
width: 2000px;
}
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