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;
}