Hello
To amend try adding the following to the Custom CSS field of your templates parameters (Extensions -> Templates -> [YourTemplateStyle] -> Custom CSS)....
(edit to taste)
.header_main {
flex-direction: column;
align-items: flex-start;
}
.hornav ul.menu > li > a,
.hornav ul.menu > li > span {
font-size: 20px;
}
Ciaran