This seems like a trivial problem, but I can\'t figure it out.
On Bootstraps own website they have the Select example.
I had the same issue and while user1732055's answer fixes the border, it removes the dropdown arrows. I solved this by removing the border from the select element and creating a wrapper span which has a border.
html:
css:
select.no-radius{
border:none;
}
.select-wrapper{
border: 1px solid black;
border-radius: 0px;
}
https://jsfiddle.net/Lrqh0drd/6/