Change font size of all elements

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

/*Title*/
[class*="header__Container-sc"] > div:nth-child(1) {
  font-size: 25px !important;
}
/*Subtitle*/
[class*="header__Container-sc"] > div:nth-child(2) {
  font-size: 25px !important;
}
/*Slider label*/
[class*="slider__Label-sc"] {
  font-size: 35px !important;
}
/*Slider label range*/
span[class*="slider__Label-sc"] {
  font-size: 25px !important;
}
/*Slider value*/
[class*="TextControlBase__TextControlBaseInput-sc"] {
  font-size: 15px !important;
}
/*Result section - titles*/
[class*="result-primary__PrimaryContainer-sc"] > div:nth-child(1) {
  font-size: 25px !important;
}
/*Result section - subtitles*/
[class*="result-primary__PrimaryContainer-sc"] > div:nth-child(3) {
  font-size: 25px !important;
}
/*Result section - values*/
[class*="result-primary__PrimaryContainer-sc"] > div:nth-child(2) * {
  font-size: 15px !important;
}
/*Result section bottomTitle*/
[class*="cta__Container-sc"] > div:nth-child(1) {
  font-size: 15px !important;
}
/*Result section bottom first paragraph*/
[class*="cta__Container-sc"] > div:nth-child(2) strong:nth-child(1) {
  font-size: 25px !important;
}
/*Result section bottom second paragraph*/
[class*="cta__Container-sc"] > div:nth-child(2) strong:nth-child(4) {
  font-size: 25px !important;
}
/*Result section button*/
[class*="ButtonBase__Ellipsis-sc"] {
  font-size: 25px !important;
}