Hi. The problem arises due to the fact that the height of the header is reduced during the scrolling.
Use the following code to exclude header from this process.
#sp-header {
position: absolute;
width: 100%;
}
And configure the padding top 100px in your Home section.
Also in Home Section there is an addon with hidden content. However, the wrapper of this addon is not hidden and has margin bottom 30px. Replace this value to 0. This will allow you to enlarge padding top on 30px in the Services section, without harm to the layout.