Hi there,

I've listed all the custom CSS in the answers below:

1. This is for the price in green and red:

.woocommerce .shop-item .item-info .price, 
.woocommerce .shop-item .item-info .woocs_price_code  {
  color: green;
}
.woocommerce .shop-item .item-info .price>del span, 
.woocommerce .shop-item .item-info .woocs_price_code>del span{
  color: red;
}

2. The cart buttons are shown in green, I cannot see any black button there.

3. Couldn't understand where you mean, please try to explain it more exactly and if possible include a screenshot/url of that part.

4. That's not possible through the theme or WordPress, you'll need any other plugin which can do that, I searched on Google and found this plugin and many others so it's up to you if you want to use them or not.

5. This is the CSS for your sale button:

.shop .shop-item .onsale {
    background: red !important;
}

6. This is the CSS code for it:

.woocommerce .place-order .button {
    background: red;
}   

Here you will find a video that tells you how you can change the theme styling through Inspect Element option, please follow it:

Hi Gasparemy,

This is the code for it, so simply change it to the color you want:

.btn.btn-primary:hover {
    background: red;
}

As shown in the video I have recorded, please follow it and see how you can do it.