How to remove whitespace on mobile version, above video background, under header on home page... HELP ME PLS!!

Site URL: https://www.beginners2runners.co.uk/

Please help me! On the mobile version, there is lots of white space above the homepage video, which is under the header. ... Also, when the website is loading the CSS is showing before the page loads under the announcement bar, can anyone help please??

#1. Try adding to Design > Custom CSS

@media screen and (max-width:767px) {
[data-section-id="62bc52cd38628f69914e5f38"] iframe {
    width: 100% !important;
    height: auto !important;
    left: 0 !important;
}
[data-section-id="62bc52cd38628f69914e5f38"] {
    min-height: unset !important;
    margin-top: -100px;
}
}

#2. Can you send all current code in Code Injection & Page Header?