Interactive Pricing Component on native JS

Hello, everyone! Thanks for checking my work :) I tried to make the whole page using only flex and, to be honest, I am very new to it. Moreover, I faced an extremely difficult problem - designing range <input>. As you can see I have not finished the thumb design and I request community help for it. I have not finished the mobile design yet but I am planning to do it as soon as possible. Thank you for attention and for feedback in advance!