fix: 19th and 20th questions replaced (freeCodeCamp#58067)

Co-authored-by: Ilenia <26656284+ilenia-magoni@users.noreply.github.com>
Co-authored-by: Sem Bauke <sem@freecodecamp.org>
Co-authored-by: Krzysztof G. <60067306+gikf@users.noreply.github.com>

curriculum/challenges/english/25-front-end-development/quiz-css-colors/66ed8fe1f45ce3ece4053eb1.md

@@ -413,91 +413,59 @@ Which color model includes the `hue` component?
 
 #### --text--
 
-Which of the following is the correct syntax to create a CSS variable with a fallback value?
+Which color function also allows you to set the opacity of the color?
 
 #### --distractors--
 
 ```css
-.element {
-  color: var(--main-color; red);
-}
+hsl(0, 20%, 30%, 50%)
 ```
 
 ---
 
 ```css
-.element {
-  color: var(--main-color);
-}
+rgb(20, 30, 80, 0.5)
 ```
 
 ---
 
 ```css
-.element {
-  color: var(--main-color: red);
-}
+rgba(20, 30, 80)
 ```
 
 #### --answer--
 
 ```css
-.element {
-  color: var(--main-color, red);
-}
+hsla(0, 20%, 30%, 50%)
 ```
 
 ### --question--
 
 #### --text--
 
-How can you use CSS variables to dynamically change the color of multiple elements?
+Which of the following is the correct way to give an element a top-to-bottom red-to-blue gradient background?
 
 #### --distractors--
 
 ```css
-:root {
-  primary-color: blue;
-}
-
-.element1, .element2 {
-  color: --primary-color;
-}
+background: radial-gradient(red, blue)
 ```
 
 ---
 
 ```css
-body {
-  --color: blue;
-}
-
-.element1, .element2 {
-  color: var(color);
-}
+background: radial-gradient(blue, red)
 ```
 
 ---
 
 ```css
-:root {
-  primary: blue;
-}
-
-.element1, .element2 {
-  color: var(--primary);
-}
+background: linear-gradient(blue, red)
 ```
 
 #### --answer--
 
 ```css
-:root {
-  --primary-color: blue;
-}
-
-.element1, .element2 {
-  color: var(--primary-color);
-}
+background: linear-gradient(red, blue)
 ```