Hello sunny,

you can resize the titles with css

.overlapping-image .slide-caption .slide-title {
    font-size: calc(1rem + 8vw);
    line-height: calc(1rem + 7.5vw);  
}

plz note that the sizes are expressed in viewport width units therefore they can be set also in pixels.

For mobile devices you can use responsive media queries

@media only screen and (max-width: 479px) {
    .overlapping-image .slide-caption .slide-title {
        font-size: calc(1rem + 14vw);
        line-height: calc(1rem + 13.5vw);
    }
}

modify the code and add it to customizer -> additional css