header color cannot be change with CSS

[issam.seghir99]

when I try to change the header color in performance > style with CSS, the headers in the epub don't change, this is what my CSS looks like :

h1 {
color : #991F95;
font-size: 2.5em;
font-weight: bold;
text-align: center;
font-family: "Monotype Corsiva", "Apple Chancery", fantasy;
border: 1px solid #ccc;
border-radius: 10px; }
h2, h3, h4 {
color : #991F95;
font-weight: bold;
text-align: center;
border: 1px solid #ccc;
border-radius: 10px; }
h2 + p:first-line {
font-variant: small-caps;
font-size: 1.1em; }