Add some improvements for carousel's buttons

[zuozas]

Tweaks carousel's buttons with small fixes and improvements

What should be done

• Add hover state. On hover button should get #303030 background color;
• Update default state color. The new default color should be #202020;
• Update progress line color. It should use the same hover state color #303030;
• Remove easing transition for the progress bar. It should be linear without any jumping at the start and slowing down at the end;

Quick preview of all states

Figma link -

https://www.figma.com/file/7MohdRwL3Cu4H8c4udzsfu/Sigmaverse-2.0?node-id=15%3A772