It’s never great to use !important
I think the reason the CSS you’re trying wasn’t taking effect is because #wrapper is used in several CSS rules… so to get more CSS specificity, you have to use #wrapper in your rule too — in addition to the actual selector you’re using.
For example:
body.page-id-6222 #wrapper .tribe-this-week-widget-wrapper .tribe-events-page-title {
font-size: 3em;
}
body.page-id-6222 #wrapper .tribe-this-week-events-widget .tribe-this-week-widget-horizontal a {
font-size: 1.1em;
color: #fff;
}
I would ordinarily not need #wrapper but that CSS wouldn’t work on your site without it.
Hopefully that CSS will help you get you the results you’re wanting — or at least help you get it there yourself.
Please let me know how it goes for you.