Change hover color on a button with Bootstrap customization

I had to add !important to get it to work. I also made my own class button-primary-override.

.button-primary-override:hover, 
.button-primary-override:active,
.button-primary-override:focus,
.button-primary-override:visited{
    background-color: #42A5F5 !important;
    border-color: #42A5F5 !important;
    background-image: none !important;
    border: 0 !important;
}

or can do this...
set all btn ( class name like : .btn- + $theme-colors: map-merge ) styles at one time :

@each $color, $value in $theme-colors {
  .btn-#{$color} {
    @include button-variant($value, $value,
    // modify
    $hover-background: lighten($value, 7.5%),
    $hover-border: lighten($value, 10%),
    $active-background: lighten($value, 10%),
    $active-border: lighten($value, 12.5%)
    // /modify
    );
  }
}

// code from "node_modules/bootstrap/scss/_buttons.scss"

should add into your customization scss file.

The color for your buttons comes from the btn-x classes (e.g., btn-primary, btn-success), so if you want to manually change the colors by writing your own custom css rules, you'll need to change:

/*This is modifying the btn-primary colors but you could create your own .btn-something class as well*/
.btn-primary {
    color: #fff;
    background-color: #0495c9;
    border-color: #357ebd; /*set the color you want here*/
}
.btn-primary:hover, .btn-primary:focus, .btn-primary:active, .btn-primary.active, .open>.dropdown-toggle.btn-primary {
    color: #fff;
    background-color: #00b3db;
    border-color: #285e8e; /*set the color you want here*/
}