40px Space in Top Bar / Nav / Logo area

Hi there.
Maybe I am missing something clearly obvious but I am attempting to find and remove the 40px gap on the left of the logo and right side of the main navigation.

<div class="inside-navigation grid-container">
...
</div>

This DIV has padding 0 40 0 40

.main-navigation.has-branding .inside-navigation.grid-container, .main-navigation.has-branding.grid-container .inside-navigation:not(.grid-container) {
  padding: 0 40px 0 40px;
}

Is that something I can change in customiser or find in the CSS?

If so, where? I can't find anything in my edits that puts a 40px gap there.

Thanks.

Martin