Add CSS transitions/animations

[gilles-margerin]

List of elements:

• navbar links underline
• react calendar
• list element in calendar event list
• partners page initial render
• pages transitions

[gilles-margerin]

list element animation

useEffect(() => {
    const liElements = document ? document.querySelectorAll(`.${styles.liItem}`) : []
    liElements.forEach((elem,i )=> {
      const timer = 100 + ((i + 1) * 200)

      elem.style.transition = `all ease-in-out ${timer}ms`
      elem.style.opacity = '1'
      elem.style.transform = 'translateY(0)'
    })

    return () => liElements.forEach(elem => {
      elem.style.opacity = '0'
      elem.style.transform = 'translateY(20px)'
    })
  })