This should probably do it... most of the code was fixed just by adding !important to each line. I had to also modify the border of the right rail and the page so they wouldn't interfere with each-other, and I think I achieved the look you were going for. I tried to add some comments to explain what each module does.
However, this might is against the customization policy, unsure though.
/* Rounds page */
.page__main {
border-radius: 20px 0px 0px 20px !important;
border:0px solid #ccc !important;
}
/* Rounds the right rail to match page */
.page__right-rail {
border-radius: 0px 20px 20px 0px !important;
border:0px solid #ccc !important;
}
/* Changes font */
.resizable-container {
font-family: "Noto Sans", sans-serif !important;
}
/* Rounds infobox */
.portable-infobox {
border-collapse: separate !important;
border-spacing: 0 !important;
border-radius: 15px !important;
overflow: hidden !important;
}
I've only tested this on one wiki, so let's hope it doesn't interfere with something on yours! Please let me know if you need help with modifying anything else!
~ halfmoonshine