General formatting

4 spaces indentation :

.ga-button {
....color: blue;

....&__icon {
........margin-left: 1rem;    
....}
}

Each opening block should be preceded by a blank line :

.ga-button {
    color: blue;
    
    /* blank */
    &__icon {
        margin-left: 1rem;    
    }
}

Each properties-value and opening block should be preceded and followed by line-break :

( even for one line declarations )

.ga-button {
    color: blue;
}