How to align buttons to bottom:

1. Make a "wrapper" container that have min-height: 100vh, display: flex, and flex-direction: column

/* 

if you have other elements on page you must subtract them from the height.

e.g. a Header with 100px: 

min-height: calc(100vh - 100px) 

*/

.wrapper {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

2. Now all the elements inside will inside the wrapper but will not take all the vertical space, use the margin-top: auto to make the desired component to take all the avaliable space.

.last-element {
  margin-top: auto;
}

Example:

Playground: