强制覆盖标准tag的css，或者标准的slds

renderedCallback() {
    //この段階で標準のコンポのスタイルを上書きします
    console.log(this.isRendered);
    if (this.isRendered) {
        return; 
    }
    this.isRendered = true;

    let style = document.createElement('style');
    style.innerText = '.slds-th__action:focus, .slds-th__action:hover {background-color: #F5C9C6; color: #000000;}';
    this.template.querySelector('c-cks_custom_table').appendChild(style);
    let style2 = document.createElement('style');
    style2.innerText = '.slds-th__action{background-color: #F5C9C6; color: #000000;}';
    this.template.querySelector('c-cks_custom_table').appendChild(style2);
    let style3 = document.createElement('style');
    style3.innerText = '.slds-scrollable_x,.slds-scrollable--x{padding-bottom:10px !important;}';
    this.template.querySelector('c-cks_custom_table').appendChild(style3);
}