cohens_h = function( prop_1, prop_2, n1, n2, ci = 0.95 ){
    x1 = asin(sign(prop_1) * sqrt(abs(prop_1)))
    x2 = asin(sign(prop_2) * sqrt(abs(prop_2)))
    es = x1 - x2
    se = sqrt(0.25 * (1 / n1 + 1 / n2 ))
    ci_diff = qnorm(1 - (1-ci) / 2) * se
    return( c( h = es*2, h_low = (es-ci_diff)*2, h_upp = (es+ci_diff)*2 ) )
}

acc1 = .70
acc2 = .90
N1 = 200
N2 = 300
cohens_h(acc1, acc2, N1, N2)

h      h_low      h_upp
-0.5157784 -0.6946978 -0.3368590