Hi Levi,
The real issue is, Adapt theme has applied "white-space: nowrap;" and that's why if width is less than the width of title, it gets hide, if you change it to "white-space: normal;", title will break into two if no more space available. However if you are ok with large screen and just wanted to fix for small devices, you can use following CSS.
@media screen and (max-width: 767px) {
#sitetitle{
font-size:18px;
white-space: normal;
text-align: left;
}
}
If you want to add it through UI go to BASEURL/admin/settings.php?section=theme_adaptable_generic and add it to the custom CSS field.
P.S: I havse set font size to 18px, you can adjust font-size as per your requirement.