vue-select Bootstrap / BootstrapVue css

component.vue

<v-select class="form-control"
  :class="{
            'is-invalid': isValid === false ? true : undefined,
            'is-valid': isValid ? true : undefined
          }"
  :options="['Canada', 'United States']">
</v-select>

vue-select.scss

:root {
    --vs-colors--lightest: #ced4da;
    --vs-colors--light: rgba(60, 60, 60, 0.5);
    --vs-colors--dark: #495057;;
    --vs-colors--darkest: rgba(0, 0, 0, 0.15);
    --vs-search-input-color: inherit;
    --vs-search-input-placeholder-color: inherit;
    --vs-font-size: 1rem;
    --vs-line-height: 1.85;
    --vs-state-disabled-bg: transparent;
    --vs-state-disabled-color: var(--vs-colors--light);
    --vs-state-disabled-controls-color: var(--vs-colors--light);
    --vs-state-disabled-cursor: default;
    --vs-border-color: var(--vs-colors--lightest);
    --vs-border-width: 1px;
    --vs-border-style: solid;
    --vs-border-radius: 4px;
    --vs-actions-padding: 4px 10px 0 3px;
    --vs-controls-color: #343a41;
    --vs-controls-size: 0.8;
    --vs-controls--deselect-text-shadow: 0 1px 0 #fff;
    --vs-selected-bg: #f0f0f0;
    --vs-selected-color: var(--vs-colors--dark);
    --vs-selected-border-color: var(--vs-border-color);
    --vs-selected-border-style: var(--vs-border-style);
    --vs-selected-border-width: var(--vs-border-width);
    --vs-dropdown-bg: #fff;
    --vs-dropdown-color: inherit;
    --vs-dropdown-z-index: 1000;
    --vs-dropdown-min-width: 160px;
    --vs-dropdown-max-height: 350px;
    --vs-dropdown-box-shadow: 0px 3px 6px 0px var(--vs-colors--darkest);
    --vs-dropdown-option-bg: #000;
    --vs-dropdown-option-color: var(--vs-dropdown-color);
    --vs-dropdown-option-padding: 3px 20px;
    --vs-dropdown-option--active-bg: #5897fb;
    --vs-dropdown-option--active-color: #fff;
    --vs-dropdown-option--deselect-bg: #fb5858;
    --vs-dropdown-option--deselect-color: #fff;
    --vs-transition-timing-function: cubic-bezier(1, -0.115, 0.975, 0.855);
    --vs-transition-duration: 150ms
}

.v-select {
    font-family: inherit;
    position: relative;
    font-size: 1rem;
}

.v-select, .v-select * {
    box-sizing: border-box;
}

:root {
    --vs-transition-timing-function: cubic-bezier(1, 0.5, 0.8, 1);
    --vs-transition-duration: 0.15s
}

@-webkit-keyframes vSelectSpinner {
    0% {
        transform: rotate(0deg)
    }
    to {
        transform: rotate(1turn)
    }
}

@keyframes vSelectSpinner {
    0% {
        transform: rotate(0deg)
    }
    to {
        transform: rotate(1turn)
    }
}

.vs__fade-enter-active, .vs__fade-leave-active {
    pointer-events: none;
    transition: opacity var(--vs-transition-duration) var(--vs-transition-timing-function)
}

.vs__fade-enter, .vs__fade-leave-to {
    opacity: 0
}

:root {
    --vs-disabled-bg: var(--vs-state-disabled-bg);
    --vs-disabled-color: var(--vs-state-disabled-color);
    --vs-disabled-cursor: var(--vs-state-disabled-cursor)
}

.vs--disabled .vs__clear, .vs--disabled .vs__dropdown-toggle, .vs--disabled .vs__open-indicator, .vs--disabled .vs__search, .vs--disabled .vs__selected {
    background-color: var(--vs-disabled-bg);
    cursor: var(--vs-disabled-cursor);
}

.v-select[dir=rtl] .vs__actions {
    padding: 0 3px 0 6px
}

.v-select[dir=rtl] .vs__clear {
    margin-left: 6px;
    margin-right: 0
}

.v-select[dir=rtl] .vs__deselect {
    margin-left: 0;
    margin-right: 2px
}

.v-select[dir=rtl] .vs__dropdown-menu {
    text-align: right
}

.vs__dropdown-toggle {
    -webkit-appearance: none;
    -moz-appearance: none;
    appearance: none;
    background: none;
    // border: var(--vs-border-width) var(--vs-border-style) var(--vs-border-color);
    border-radius: var(--vs-border-radius);
    display: flex;
    padding: 0 0 2px 0;
    white-space: normal;
    margin-top: -6px;
    margin-left: -12px;
    margin-right: -12px;
    min-width: 100px;
    // border: 1px solid #01bcd4;
    color: #495057;
}

.vs__selected-options {
    display: flex;
    flex-basis: 100%;
    flex-grow: 1;
    flex-wrap: wrap;
    padding: 0 2px;
    position: relative
}

.vs__actions {
    align-items: center;
    display: flex;
    padding: var(--vs-actions-padding);
}

.vs--searchable .vs__dropdown-toggle {
    cursor: text
}

.vs--unsearchable .vs__dropdown-toggle {
    cursor: pointer
}

.vs--open .vs__dropdown-toggle {
    border-bottom-color: transparent;
    border-bottom-left-radius: 0;
    border-bottom-right-radius: 0;
}

.vs__open-indicator {
    fill: var(--vs-controls-color);
    transform: scale(var(--vs-controls-size));
    transition: transform var(--vs-transition-duration) var(--vs-transition-timing-function);
    transition-timing-function: var(--vs-transition-timing-function);
}

.vs--open .vs__open-indicator {
    transform: rotate(180deg) scale(var(--vs-controls-size))
}

.vs--loading .vs__open-indicator {
    opacity: 0
}

.vs__clear {
    fill: var(--vs-controls-color);
    background-color: transparent;
    border: 0;
    cursor: pointer;
    margin-right: 8px;
    margin-bottom: 3px;
    padding: 0;
    transform: scale(var(--vs-controls-size));
}

.vs__dropdown-menu {
    background: var(--vs-dropdown-bg);
    border: var(--vs-border-width) var(--vs-border-style) var(--vs-border-color);
    border-radius: 0 0 var(--vs-border-radius) var(--vs-border-radius);
    border-top-style: none;
    box-shadow: var(--vs-dropdown-box-shadow);
    box-sizing: border-box;
    color: var(--vs-dropdown-color);
    display: block;
    left: 0;
    list-style: none;
    margin: 0;
    max-height: var(--vs-dropdown-max-height);
    min-width: var(--vs-dropdown-min-width);
    overflow-y: auto;
    padding: 5px 0;
    position: absolute;
    text-align: left;
    top: calc(100% - var(--vs-border-width));
    width: 100%;
    z-index: var(--vs-dropdown-z-index)
}

.vs__no-options {
    text-align: center
}

.vs__dropdown-option {
    clear: both;
    color: var(--vs-dropdown-option-color);
    cursor: pointer;
    display: block;
    line-height: 1.42857143;
    padding: var(--vs-dropdown-option-padding);
    white-space: nowrap
}

.vs__dropdown-option--highlight {
    background: var(--vs-dropdown-option--active-bg);
    color: var(--vs-dropdown-option--active-color)
}

.vs__dropdown-option--deselect {
    background: var(--vs-dropdown-option--deselect-bg);
    color: var(--vs-dropdown-option--deselect-color)
}

.vs__dropdown-option--disabled {
    background: var(--vs-state-disabled-bg);
    color: var(--vs-state-disabled-color);
    cursor: var(--vs-state-disabled-cursor)
}

.vs__selected {
    align-items: center;
    background-color: var(--vs-selected-bg);
    border: var(--vs-selected-border-width) var(--vs-selected-border-style) var(--vs-selected-border-color);
    border-radius: var(--vs-border-radius);
    color: var(--vs-selected-color);
    display: flex;
    line-height: var(--vs-line-height);
    margin: 2px 2px 0;
    padding: 0 .25em;
    z-index: 0;
}

.vs__deselect {
    fill: var(--vs-controls-color);
    -webkit-appearance: none;
    -moz-appearance: none;
    appearance: none;
    background: none;
    border: 0;
    cursor: pointer;
    display: inline-flex;
    margin-left: 4px;
    padding: 0;
    text-shadow: var(--vs-controls--deselect-text-shadow)
}

.vs--single .vs__selected {
    background-color: transparent;
    border-color: transparent
}

.vs--single.vs--loading .vs__selected, .vs--single.vs--open .vs__selected {
    opacity: .4;
    position: absolute
}

.vs--single.vs--searching .vs__selected {
    display: none
}

.vs__search::-webkit-search-cancel-button {
    display: none
}

.vs__search::-ms-clear, .vs__search::-webkit-search-decoration, .vs__search::-webkit-search-results-button, .vs__search::-webkit-search-results-decoration {
    display: none
}

.vs__search, .vs__search:focus {
    -webkit-appearance: none;
    -moz-appearance: none;
    appearance: none;
    background: none;
    border: 1px solid transparent;
    border-left: none;
    box-shadow: none;
    color: var(--vs-search-input-color);
    flex-grow: 1;
    font-size: var(--vs-font-size);
    line-height: var(--vs-line-height);
    max-width: 100%;
    outline: none;
    // padding: 0 7px;
    width: 0;
    z-index: 1;
}

.vs__search::-moz-placeholder {
    color: var(--vs-search-input-placeholder-color)
}

.vs__search:-ms-input-placeholder {
    color: var(--vs-search-input-placeholder-color)
}

.vs__search::placeholder {
    color: var(--vs-search-input-placeholder-color)
}

.vs--unsearchable .vs__search {
    opacity: 1
}

.vs--unsearchable:not(.vs--disabled) .vs__search {
    cursor: pointer
}

.vs--single.vs--searching:not(.vs--open):not(.vs--loading) .vs__search {
    opacity: .2
}

.vs__spinner {
    align-self: center;
    -webkit-animation: vSelectSpinner 1.1s linear infinite;
    animation: vSelectSpinner 1.1s linear infinite;
    border: .9em solid hsla(0, 0%, 39%, .1);
    border-left-color: rgba(60, 60, 60, .45);
    font-size: 5px;
    opacity: 0;
    overflow: hidden;
    text-indent: -9999em;
    transform: translateZ(0) scale(var(--vs-controls--spinner-size, var(--vs-controls-size)));
    transition: opacity .1s
}

.vs__spinner, .vs__spinner:after {
    border-radius: 50%;
    height: 5em;
    transform: scale(var(--vs-controls--spinner-size, var(--vs-controls-size)));
    width: 5em
}

.vs--loading .vs__spinner {
    opacity: 1
}

.v-select:focus-within {
    color: #495057;
    background-color: #fff;
    border-color: #80bdff;
    outline: 0;
    box-shadow: 0 0 0 0.2rem rgba(0, 123, 255, 0.25);
}

.v-select.is-valid:focus-within {
    border-color: #28a745;
    box-shadow: 0 0 0 0.2rem rgba(40, 167, 69, 0.25);
}

.v-select.is-invalid:focus-within {
    border-color: #dc3545;
    box-shadow: 0 0 0 0.2rem rgba(220, 53, 69, 0.25);
}

.v-select.vs--disabled {
    background-color: #e9ecef;
    opacity: 1;
}