I am trying to extend Bootstrap. I do not want to touch any of the Bootstrap core files, so I have created my own styles.scss and in there I have the following:
@import "custom/variables";
@import "../../node_modules/bootstrap-sass/assets/stylesheets/bootstrap";
@import "custom/modular-styles";
In _variables.scss I am overwriting some of the variables (e.g. getting rid of rounded corners).
In _modular-styles.scss I call various other SASS partials that I want to customise (e.g. _forms.scss).
In _forms.scss here is what I've done:
.form-control {
    display: block;
    width: 100%;
    height: $input-height-base;
    padding: $padding-base-vertical $padding-base-horizontal;
    font-size: $font-size-base;
    line-height: $line-height-base;
    color: $input-color;
    background-color: $input-bg;
    background-image: none;
    border: 1px solid $input-border;
    border-radius: $input-border-radius;
    box-shadow: none; // this use to be @include box-shadow(inset 0 1px 1px rgba(0,0,0,.075));
    @include transition(border-color ease-in-out .15s, box-shadow ease-in-out .15s);
    outline: none; // this use to be @include form-control-focus;
    @include placeholder;
    &::-ms-expand {
        border: 0;
        background-color: transparent;
    }
    &:focus {
        outline: none;
    }
    &[disabled],
    &[readonly],
    fieldset[disabled] & {
        background-color: $input-bg-disabled;
        opacity: 1;
    }
    &[disabled],
    fieldset[disabled] & {
        cursor: $cursor-disabled;
    }
}
Shouldn't that work? Yet I am still seeing the outline glow when an input is on :focus
 
     
     
     
     
     
     
    