For modals, we USUALLY use something like this:
//CSS Code
#modal {
width: 100%;
height: 0%;
}
and then with JavaScript, we just make the height to 100% when we display the modal.
Now there are few ways to display the modal from bottom. We can use margin-top directly or we can use animation to do the same with animation effect. I am going to discuss the first method.
Solution: Using margin-top
//CSS Code
#modal {
width: 100%;
height: 0%;
margin-top:100%;
}
After that using JavaScript, remove the margin-top by setting it's value to zero along with changing the height to 100%.
display modal transition vertically