CSS voice-rate Speech Media property

The CSS voice-rate property specifies the speaking rate in words per minute. Set the rate with the following values

voice-rate: [normal | x-slow | slow | medium | fast | x-fast]

Above, if you want slow voice rate, then set slow; for slower, set x-slow.

Set faster voice rate:
p {
   voice-rate: x-fast;
}

Set voice rate in percentage

p {
   voice-rate: 40%;
}