Set Scratch UI to black

scratch_fullscreen_cover.js

{
    // sets everything but stage to black on full-screened https://scratch.mit.edu/projects/editor/

    const stage = document.querySelector('[class^="stage_stage-bottom-wrapper"]')

    const rect = stage.getBoundingClientRect();
    
    const pageHeight = document.documentElement.scrollHeight;

    var leftCover = document.createElement('div');
    leftCover.setAttribute('style',`
        position: absolute;
        left: 0;
        top: 0;
        width: ${rect.left}px;
        height: ${pageHeight}px;
        background-color: black;
        z-index: 999999;
    `)
    document.body.appendChild(leftCover)

    var topCover = document.createElement('div');
    topCover.setAttribute('style', `
        position: absolute;
        top: 0;
        left: 0;
        width: 100%;
        height: ${rect.top}px;
        background-color: black;
        z-index: 999999;
    `)
    document.body.appendChild(topCover)

    var bottomCover = document.createElement('div');
    bottomCover.setAttribute('style', `
        position: absolute;
        left: ${rect.left}px;
        top: ${rect.bottom}px;
        width: 100%;
        height: ${pageHeight}px;
        background-color: black;
        z-index: 999999;
    `)
    document.body.appendChild(bottomCover)
    
    var rightCover = document.createElement('div');
    bottomCover.setAttribute('style', `
        position: absolute;
        left: ${rect.right}px;
        top: 0;
        width: 100%;
        height: ${pageHeight}px;
        background-color: black;
        z-index: 999999;
    `)
    document.body.appendChild(rightCover)
}