How can we scroll sub-menu of Front Page menu

Please look at https://home-tuition.sg

Two issues:

1. On the front page is the Front Page Menu. If you put your cursor over the option “Insights”, a long sub-menu appears. There are 9 pages and a custom link in this sub-menu. I notice that the full sub-menu does not appear, i.e. I can only see the top 7/8 items, the bottom items cannot be seen. It is worse when I view with a mobile phone. When I scrolled with my mouse, the main page moves down, but the sub-menu stays static. Is there anything I can do about this? Is it possible to code for the sub-menu, instead of the entire webpage, to scroll when my mouse is over the sub-menu? Or is it possible to include a scroll bar on a sub-menu? Or is it possible to break up the arrangement of a sub-menu into 2 columns?

2. I tried to justify the sentences and to make the fonts the same size on the front page. Below is the custom CSS I pasted into the Stylesheet (style.css) of the child theme. I see no effect at all. Can you let me know if they are correct?

.feature-column > .container > .row {
display: flex;
}
.feature-col-item p {
font-size: 16px !important;
text-align: justify !important;
}
.testimonial-content p {
font-size: 16px !important;
text-align: justify !important;
}

Thank you.