.form-signin {
    max-width: 300px;
    margin: 0 auto;
    position: absolute;
    top: 50%;
    transform: translateY(-165px);
    left: 40%;
    background: $blue_light3;
    padding: 20px;
    border-radius: 10px;

    .form-signin-heading {
        font-weight: 300;
        text-transform: uppercase;
        letter-spacing: 2px;
        text-align: center;
        margin: 5px 0 26px;
        color: $navy_drk2;
    }

    input { background: white; }
}
.form-signin {
    max-width: 300px;
    margin: 0 auto;
    position: absolute;
    transform: translate(-142px, -165px);
    top: 50%;
    left: 50%;
    background: $blue_light3;
    padding: 20px;
    border-radius: 10px;

    .form-signin-heading {
        font-weight: 300;
        text-transform: uppercase;
        letter-spacing: 2px;
        text-align: center;
        margin: 5px 0 26px;
        color: $navy_drk2;
    }

    input { background: white; }
}

Adjust horizontal alignment of sign in modal
Adjust horizontal alignment of sign in modal
