If you’re having trouble with your CSS border not showing up, there are a few things you can check.
First, make sure that the element you’re trying to apply the border to is set to
display: block; or
display: inline-block;. If the HTML element is set to
display: none it’s invisible and thus you won’t be able to see it’s border.
Next, check your CSS code to make sure that you’re using the correct property for the border (
border-color) and that it’s applied to the right element. That’s the most common issue as even a single character difference can break your CSS selector.
Finally, make sure that your browser is up-to-date and that you don’t have any browser extensions or plugins interfering with your CSS.