Align items in middle in CSS

I have a html code and i want to align theme like the image below:
aligned image

My html code:

<button class="container">
    <span class="btn__img"></span>
    <span class="btn__txt">Basic</span>
</button>

>Solution :

.container{
    display: flex;
    flex-direction: column;
    justify-content: center; // if you want to align it center vertically 
    align-items: center; // if you want to align it center horizontally
}

Apply this css to your button.