Change size of all elements

Add this code to the Custom CSS field on the Style tab of your Weather widget’s settings:

.eapp-weather-detail-locationName {
  font-size: 20px;
}

.eapp-weather-detail-currentTemp {
  font-size: 20px;
}

.eapp-weather-detail-weatherName {
  font-size: 20px;
}

.eapp-weather-forecast-detail-component * {
  font-size: 20px;
}

.eapp-weather-forecast-item-date {
  font-size: 20px;
}

.eapp-weather-forecast-item-temp {
  font-size: 20px;
}

.eapp-weather-daily-item-date {
  font-size: 20px;
}

.eapp-weather-daily-item-day {
  font-size: 20px;
}

.eapp-weather-daily-item-max {
  font-size: 20px;
}

.eapp-weather-daily-item-min {
  font-size: 20px;
}