Hello Chokri
Our technical team has resolved the header issue.
About the slider caption hiding behind the header > you need to choose a larger size image like we used a 1600(width)x625(height) image. This will increase the space for the content. because you are using too much content in the slider. if you allow us to let the design of caption/description of slider to align bit more to the left then it will create more space for the description our technical team will do that for you if you allow us to do so. which may take some of your time. If you simply use an image with more height then it will solve your issue.
Let us know what your views are.
Thank you