A vivaldi custom css

main.scss

.bookmark-bar {
  height: 32px;
  padding-inline-start: 0.5rem;
  padding-inline-end: 0.5rem;
  padding-block-start: 0.25rem;
  padding-block-end: 0.5rem;
  position: relative;
  font-size: 12px;
}

.bookmark-bar.default:before {
  width: 100%;
  height: 1px;
  background: var(--colorBg);
  position: absolute;
  top: -1px;
  z-index: 90;
  content: "";
  left: 0;
}

.toolbar-mainbar {
  height: 2.375rem;
}

.toolbar-mainbar.UrlBar {
  padding-inline-start: 0.25rem;
  padding-inline-end: 0.5rem;
}

.UrlBar-SearchField,
.UrlBar-AddressField {
  height: 1.875rem;
  padding-inline-start: 0.5rem;
  padding-inline-end: 0.5rem;
}

.button-toolbar {
  align-self: auto;
}

.close {
  background-color: transparent;
}

.tab-position .tab:not(.active) {
  border-top-left-radius: 0;
  border-top-right-radius: 0;
  border-right: 1px solid #37415125;
}

.button-toolbar.toggle-trash {
  transform: translate(-2px, -1px);
}

.button-badge {
  align-items: stretch;
}

.tab .button-badge {
  top: 1px;
  left: 16px;
}

.toolbar-large .button-toolbar > button > .button-badge {
  top: 1px;
  left: 18px;
}

/* Changing next page icon  - $mainbarNewNextPageIcon */
.toolbar-mainbar .button-toolbar svg path[d^="M9.29289 19.2929C8.90237 19.6834 8.90237"] {
  d: path(
    "m 13.868201,5.2190488 c -0.124432,0.006 -0.242143,0.058241 -0.330078,0.1464844 -0.195212,0.1952535 -0.195212,0.5117777 0,0.7070312 l 6.427735,6.4277346 H 4.8271858 a 0.5,0.5 0 0 0 -0.5,0.5 0.5,0.5 0 0 0 0.5,0.5 H 19.965858 l -6.427735,6.427734 c -0.195212,0.195254 -0.195212,0.511778 0,0.707032 0.195254,0.195212 0.511778,0.195212 0.707032,0 l 7.28125,-7.28125 a 0.50000004,0.50000004 0 0 0 0,-0.707032 L 14.245155,5.3655332 C 14.145738,5.265801 14.008874,5.2126157 13.868201,5.2190488 Z"
  );
}

/* Changing back page icon - $mainbarNewBackPageIcon */
.toolbar-mainbar .button-toolbar svg path[d^="M15.2929 20.7071C15.6834 21.0976 16.3166"] {
  d: path(
    "m 12.131799,5.2190488 c 0.124432,0.006 0.242143,0.058241 0.330078,0.1464844 0.195212,0.1952535 0.195212,0.5117777 0,0.7070312 L 6.034142,12.500299 h 15.138672 a -0.5,0.5 0 0 1 0.5,0.5 -0.5,0.5 0 0 1 -0.5,0.5 H 6.034142 l 6.427735,6.427734 c 0.195212,0.195254 0.195212,0.511778 0,0.707032 -0.195254,0.195212 -0.511778,0.195212 -0.707032,0 l -7.28125,-7.28125 a -0.50000004,0.50000004 0 0 1 0,-0.707032 l 7.28125,-7.2812498 c 0.09942,-0.099732 0.236281,-0.1529175 0.376954,-0.1464844 z"
  );
}

/* Changing refresh icon - $mainbarNewRefreshIcon */
.button-toolbar svg path[d^="M20 6.20711C20 5.76166 19.4614 5.53857 19.1464 5.85355L17.2797"] {
  d: path(
    "M6.062 12.05a7 7 0 0 1 12.55-3.22l.13.17h-3.25a.5.5 0 1 0 0 1h4a.5.5 0 0 0 .5-.5v-4a.5.5 0 0 0-1 0v2.2a8 8 0 1 0 1.99 4.77.502.502 0 1 0-1 .08 7 7 0 1 1-13.92-.5z"
  );
}
/* Changing cancel load icon - $mainbarNewCancelLoadIcon */
.button-toolbar svg path[d^="M8.70711 7.29289C8.31658 6.90237 7.68342 6.90237 7.29289"] {
  d: path(
    "M5.436 5a.47.47 0 0 0-.297.139.47.47 0 0 0 0 .664L12.336 13l-7.197 7.197a.47.47 0 0 0 0 .664.47.47 0 0 0 .664 0L13 13.664l7.197 7.197a.47.47 0 0 0 .664 0 .47.47 0 0 0 0-.664L13.664 13l7.197-7.197a.47.47 0 0 0 0-.664.47.47 0 0 0-.308-.139.47.47 0 0 0-.356.139L13 12.336 5.803 5.139A.47.47 0 0 0 5.494 5a.47.47 0 0 0-.058 0z"
  );
}

/* Changing homepage icon - $mainbarNewHomepageIcon */
.button-toolbar svg path[d^="M14.0607 5.14645C13.4749 4.56066 12.5251 4.56066 11.9393"] {
  d: path(
    "M12 5.89a1.5 1.5 0 0 1 2 0l5.5 4.94c.32.28.5.69.5 1.11V19c0 .83-.67 1.5-1.5 1.5H16a1.5 1.5 0 0 1-1.5-1.5v-3.5a.5.5 0 0 0-.5-.5h-2a.5.5 0 0 0-.5.5V19c0 .83-.67 1.5-1.5 1.5H7.5A1.5 1.5 0 0 1 6 19v-7.06c0-.42.18-.83.5-1.11zm1.33.74a.5.5 0 0 0-.66 0l-5.5 4.94a.5.5 0 0 0-.17.37V19c0 .27.22.5.5.5H10a.5.5 0 0 0 .5-.5v-3.5c0-.83.67-1.5 1.5-1.5h2c.83 0 1.5.67 1.5 1.5V19c0 .27.22.5.5.5h2.5a.5.5 0 0 0 .5-.5v-7.06a.5.5 0 0 0-.17-.37z"
  );
}