When using “height: 100vh” for the container, vertical scrollbar appears

By default body and html are assigned to margin or padding to some pixels. Try using following code.

1vh = 1% of veiwport height
100vh = 100% of height.

So never calculate height – 3px. like this

body,html {
    margin: 0;
    padding: 0;
}
* {
    box-sizing: border-box;
}