I made my own theme from the blue FoldableTheme and called it myblue. I notice that although the popups are styled with my blue color, the mobile popups are not. I tried adding this to the myblue/style.css, but it didn't work:
.esriPopupMobile .titlePane {
background-color: #CBDDEB;
}
I added important to the color, but it didn't make any difference. I'm confused why I was able to easily override esri.Popup .titlePane with my own color, but adding .esriPopupMobile .titlePane had no effect.