weis nicht wozu dieser CSS Code ist

/*Tabs eckig, no margin, color not active*/

#TabsToolbar #alltabs-button
{
    display: none !important;
}

#TabsToolbar .tabbrowser-tab .tab-background
{
    border-radius: unset !important;
    margin-block: unset !important;
}

.tabbrowser-tab:not([visuallyselected="true"])
{
    background-color: #A3A3A3 !important;
    border-right: 1px solid #444 !important;
    border-bottom: 1px solid #444 !important;
    border-top: 2px solid transparent !important;
}

.tabbrowser-tab:not([visuallyselected="true"]):hover
{
    border-top: 2px solid #757575 !important;
}

.tabbrowser-tab[visuallyselected="true"]
{
    border-top: 2px solid #0A84FF !important;
}

.tabbrowser-tab .tab-background[selected="true"] {
    background-color: #F9F9FA !important;
}


.tabbrowser-tab
{
    padding-inline: unset !important;
}

    /* Tabs rund und farbig */

    /* Angaben für die TAB-Leiste*/

    /* TAB normal (inaktiv):
    * Hintergrundfarbe, Schriftfarbe,
    * Rahmen um die Tabs, oben abgerundet und Abstände angepasst,
    * unten kein Rahmen -> Abschlussrahmen vom Container.*/

    
    #TabsToolbar .tabbrowser-tab {
    color: black !important;
    border: 1px solid !important;
    border-bottom: 1px solid black !important;
    border-radius: 14px 14px !important;
    margin-top: 0px !important;
    padding: 0px 0 !important;  }

    /* TAB bei bei angewähltem TAB (aktiv):
    * Hintergrundfarbe, Rahmen,
    * Schriftfarbe.*/
 
    #TabsToolbar .tabbrowser-tab[selected="true"] {
    background: red !important;
    font-weight:bold !important;
    color: black ! important; }

    /* Tab-Icon etwas größer,
    * links weniger, unten etwas mehr Abstand zum TAB-Rand.*/
 
    #TabsToolbar .tab-icon-image {
    height: 22px !important;
    width:  22px !important;
    margin-left: 5px !important;
    margin-bottom: 0px !important; }
        
    /* Tab-Schließen-Button:
    * Rechts weniger Abstand zum TAB-Rand, etwas größer,
    * Textfarbe (Kreuz)
    * Hintergrundfarbe, an den Eckenradius des Buttons angepaßt.*/
 
    #TabsToolbar .tab-close-button {
    margin-right: 1px !important;
    padding: 0 !important;
    color: black !important; }

    #TabsToolbar .tab-close-button .toolbarbutton-icon {
    height: 18px !important;
    width:  18px !important;
    background-color: red !important;
    border-radius: 5px !important; }
    

    /* Schliessen-Button nur, wenn angewählt */

    tab:not([selected]) .tab-close-button {display: none !important; }

    /* Alle anderen Elemente in den TABs ohne Hintergrund. */

    #TabsToolbar .tabbrowser-tab * {
    background: none !important; } 
 

    /* Schriftgröße Tabs */

    .tab-text {
    font-size:15px !important; }
    
    /*Damit wird der Tabtext am Ende nicht ausgeblendet*/
    .tab-label-container[textoverflow][labeldirection=ltr]:not([pinned]),
    .tab-label-container[textoverflow]:not([labeldirection]):not([pinned]):-moz-locale-dir(ltr) {
    direction: ltr;
    mask-image: linear-gradient(to left, transparent, black 0em) !important; }
    
    /* Doppelte Schliessung ausblenden */

    #TabsToolbar > .titlebar-buttonbox-container {
    display:none !important; }    

    /* Tabs Proton-Design */

    :root {
    --proton-tab-radius: 0px !important;
    --proton-tab-block-margin: 0px !important;
    --inline-tab-padding: 10px !important; 
    }

    #TabsToolbar {
    min-height: 36px !important;
    max-height: 36px !important;
    border-top: 1px solid #B2B2B2 !important;
    border-bottom: 1px solid #B2B2B2 !important; 
    margin-bottom: 1px !important;
    padding-left: 2px !important;}

    #TabsToolbar .toolbarbutton-1 {
    margin-top: 2px !important;
    margin-bottom: 2px !important;}

    #TabsToolbar .toolbarbutton-1 > image {
    padding: 2px 4px !important;}

    #TabsToolbar:not([brighttext]) #tabbrowser-tabs:not([noshadowfortests]) .tabbrowser-tab:is([visuallyselected="true"], [multiselected]) > .tab-stack > .tab-background {
    box-shadow: none !important;}

    .tabbrowser-tab {
    box-shadow: none !important;
    margin-right: 0 !important;}
    
    #tabbrowser-tabs:not([positionpinnedtabs]) > 
    #tabbrowser-arrowscrollbox > 
    .tabbrowser-tab[pinned] + 
    .tabbrowser-tab:not([pinned]) {
    margin-inline-start: 6px !important;}

    .tabbrowser-tab .tab-content {
    background-image: linear-gradient(to bottom, dimgrey 0%, dimgrey 14%, dimgrey 14%, dimgrey 100%) !important;
    padding: 0 3px !important;
    margin-top: 2px !important;
    margin-bottom: 1px !important;}
    
    .tabbrowser-tab[selected="true"] .tab-content {
    background-image: linear-gradient(to bottom, green 0%, green 14%, dimgrey 14%, dimgrey 100%) !important;
    margin-top: 2px !important;
    margin-bottom: 1px !important;}
    
    .tabbrowser-tab:hover .tab-content {
    background-image: linear-gradient(to bottom, saddlebrown 0%, saddlebrown 14%, saddlebrown 14%, saddlebrown 100%) !important;}
    
    .tabbrowser-tab[selected="true"]:hover .tab-content {
    background-image: linear-gradient(to bottom, green 0%, green 14%, saddlebrown 14%, saddlebrown 100%) !important;} 

    .tab-throbber:not([pinned]),
    .tab-sharing-icon-overlay:not([pinned]),
    .tab-icon-pending:not([pinned]),
    .tab-icon-image:not([pinned]) {
    margin-top: 2px !important;
    margin-inline-end: 5px !important;}

    .tabbrowser-tab .tab-content .tab-text.tab-label,
    .tabbrowser-tab:hover .tab-content .tab-text.tab-label {
    margin-top: 1px !important;}

    /* Rahmen um die Tableiste durchsichtig */

    #TabsToolbar {
    border: 0.2px solid transparent !important;}
     
    #TabsToolbar:hover {
    border: 0.2px solid transparent !important;}     

    .tabbrowser-tab[label*=" - YouTube"] .tab-content,
    .tabbrowser-tab[label*="YouTube - youtube.com"] .tab-content {
    background-image: linear-gradient(to bottom, red 0%, red 14%, red 14%, red 100%) !important;}
    
    .tabbrowser-tab[label*=" - YouTube"][selected="true"] .tab-content,
    .tabbrowser-tab[label*="YouTube - youtube.com"][selected="true"] .tab-content {
    background-image: linear-gradient(to bottom, green 0%, green 14%, red 14%, red 100%) !important;}
    
    .tabbrowser-tab[label*=" - YouTube"]:hover .tab-content,
    .tabbrowser-tab[label*="YouTube - youtube.com"]:hover .tab-content {
    background-image: linear-gradient(to bottom, saddlebrown 0%, saddlebrown 14%, saddlebrown 14%, saddlebrown 100%) !important;}
    
    .tabbrowser-tab[label*=" - YouTube"][selected="true"]:hover .tab-content,
    .tabbrowser-tab[label*="YouTube - youtube.com"][selected="true"]:hover .tab-content {
    background-image: linear-gradient(to bottom, green 0%, green 14%, saddlebrown 14%, saddlebrown 100%) !important;}

    .tabbrowser-tab .tab-content vbox.tab-label-container.proton {
    -moz-box-orient: horizontal !important;} 
    
    .tabbrowser-tab .tab-content vbox.tab-label-container.proton hbox.tab-icon-sound {
    margin-top: 3px !important;
    margin-right: 0px !important;} 
    
    .tab-icon-sound[soundplaying="true"],
    .tab-icon-sound[muted="true"],
    .tab-icon-sound[activemedia-blocked="true"] {
    background: #FFF !important;
    padding: 0 1px !important;}
    
    .tab-icon-sound[soundplaying="true"] .tab-icon-sound-image,
    .tab-icon-sound[muted="true"] .tab-icon-sound-image,
    .tab-icon-sound[activemedia-blocked="true"] .tab-icon-sound-image {
    fill: #F10 !important;}

    .tab-icon-sound-image {
    height: 1.9em !important;}
    
    .tabbrowser-tab .tab-content vbox.tab-label-container.proton label[class="tab-icon-sound-label tab-icon-sound-blocked-label"],
    .tabbrowser-tab .tab-content vbox.tab-label-container.proton label[class="tab-icon-sound-label tab-icon-sound-playing-label"],
    .tabbrowser-tab .tab-content vbox.tab-label-container.proton label[class="tab-icon-sound-label tab-icon-sound-muted-label"] {
    display: none !important;}

    /* Tab Beschriftung mittig */
    
    .tab-content {
    display: flex !important; 
    justify-content: center !important;
    align-items: center !important;}

    .tab-label-container {
    margin: auto !important;}

    .tabbrowser-tab > .tab-stack > .tab-content > .tab-close-button {
    flex-shrink: 0 !important; 
    padding: 0px !important;
    width: 16px !important;}

    /* Tab Mindestbreite einstellen */
    
    .tabbrowser-tab:not([pinned]) {
    -moz-box-flex: 0 !important;
    min-width: 250px !important;
}