Make a simple adjustment in the 'head' section of your HTML by changing the order of the local CSS file and the Bootstrap CSS. Ensure that the local CSS is placed after the Bootstrap CSS:
<head>
<!-- Bootstrap CSS comes first -->
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css" integrity="sha384-ggOyR0iXCbMQv3Xipma34MD+dH/1fQ784/j6cY/iJTQUOhcWr7x9JvoRxT2MZw1T" crossorigin="anonymous">
<!-- Local CSS should be last -->
<link rel="stylesheet" href="style.css">
</head>
If you have applied !important in your CSS, it should now take effect properly.
Alternatively, you can also apply your CSS inline using
<element style="padding:0"></element>