Hello @nadatouma !
Here is a step-by-step instruction that can help you to find the place where you can change the arrow scroll color arrow to red.
Please, test changes in a theme copy first vs editing the live theme (unless you are really sure it will work). Duplicate the theme and test things in the copy.
Follow these steps:
/================ Slider arrows ================/
transition: opacity 0.15s ease-in;
Replace a current color variable "$color-body-text" with red: "#f00000". You can add another one color value that you need.
You can change an arrow opacity in the 3820 line and a hover in the 3831 line.
Hope this helps!