om/node_modules/buefy/src/scss/components/_modal.scss

.modal {
    &.is-full-screen {
        .animation-content,
        .modal-card {
            width: 100%;
            height: 100%;
            max-height: 100vh;
            margin: 0;
            background-color: #ffffff;
        }
    }
    .animation-content {
        margin: 0 20px;
        .modal-card {
            margin: 0;
        }
        @include mobile {
            width: 100%;
        }
    }
    .modal-content {
        width: 100%;
    }
}