chrome/browser/resources/new_tab_page/customize_themes.html

<style>
  #thirdPartyThemeContainer {
    width: 100%;
  }

  #thirdPartyTheme {
    align-items: center;
    border-radius: 5px;
    border: 1px solid var(--ntp-border-color);
    color: var(--ntp-primary-text-color);
    display: flex;
    flex-direction: row;
    margin-bottom: 24px;
    padding: 0 16px;
  }

  #thirdPartyBrushIcon {
    -webkit-mask-image: url(icons/brush.svg);
    -webkit-mask-repeat: no-repeat;
    -webkit-mask-size: 100%;
    background-color: var(--ntp-primary-text-color);
    height: 24px;
    margin-inline-end: 20px;
    width: 24px;
  }

  #thirdPartyThemeNameContainer {
    flex-grow: 1;
    margin-inline-end: 24px;
  }

  #thirdPartyThemeName {
    font-weight: bold;
  }

  #thirdPartyLink {
    -webkit-mask-image: url(chrome://resources/images/open_in_new.svg);
    -webkit-mask-repeat: no-repeat;
    -webkit-mask-size: 100%;
    background-color: var(--ntp-primary-text-color);
    height: 20px;
    margin-inline-end: 24px;
    width: 20px;
  }

  #uninstallThirdPartyButton {
    margin: 16px 0;
  }

  #themesContainer {
    --ntp-grid-gap: 20px;
    padding: 3px;
  }

  #themesContainer > * {
    outline-width: 0;
  }

  :host-context(.focus-outline-visible) #themesContainer > *:focus {
    box-shadow: 0 0 0 2px rgba(var(--google-blue-600-rgb), .4);
  }

  #autogeneratedThemeContainer {
    display: flex;
    position: relative;
  }

  #colorPickerIcon {
    -webkit-mask-image: url(icons/colorize.svg);
    -webkit-mask-repeat: no-repeat;
    -webkit-mask-size: 100%;
    background-color: var(--google-grey-refresh-700);
    height: 20px;
    left: calc(50% - 10px);
    position: absolute;
    top: calc(50% - 10px);
    width: 20px;
  }

  #autogeneratedTheme {
    --ntp-theme-icon-frame-color: var(--google-grey-refresh-100);
    --ntp-theme-icon-active-tab-color: white;
    --ntp-theme-icon-stroke-color: var(--google-grey-refresh-300);
  }

  #defaultTheme {
    --ntp-theme-icon-frame-color: rgb(222, 225, 230);
    --ntp-theme-icon-active-tab-color: white;
  }

  @media (prefers-color-scheme: dark) {
    #defaultTheme {
      --ntp-theme-icon-frame-color: rgb(var(--google-grey-900-rgb));
      --ntp-theme-icon-active-tab-color: rgb(50, 54, 57);
    }
  }

</style>
<div id="thirdPartyThemeContainer" hidden="[[!isThirdPartyTheme_(theme)]]">
  <div id="thirdPartyTheme">
    <div id="thirdPartyBrushIcon"></div>
    <div id="thirdPartyThemeNameContainer">
      <div id="thirdPartyThemeName" >
        [[theme.info.thirdPartyThemeInfo.name]]
      </div>
      <div>
        $i18n{thirdPartyThemeDescription}
      </div>
    </div>
    <a id="thirdPartyLink" target="_blank"
        href$="[[getThirdPartyLink_(theme.info.thirdPartyThemeInfo.id)]]">
    </a>
    <cr-button id="uninstallThirdPartyButton"
        on-click="onUninstallThirdPartyThemeClick_">
      $i18n{uninstallThirdPartyThemeButton}
    </cr-button>
  </div>
</div>
<input id="colorPicker" type="color" on-change="onCustomFrameColorChange_"
    hidden>
</input>
<ntp-grid id="themesContainer" columns="6">
  <div id="autogeneratedThemeContainer" tabindex="0"
      on-click="onAutogeneratedThemeClick_">
    <ntp-theme-icon id="autogeneratedTheme" title="$i18n{colorPickerLabel}"
        selected$="[[isThemeIconSelected_('autogenerated', theme)]]">
    </ntp-theme-icon>
    <div id="colorPickerIcon"></div>
  </div>
  <ntp-theme-icon id="defaultTheme" title="$i18n{defaultThemeLabel}"
      on-click="onDefaultThemeClick_" tabindex="0"
      selected$="[[isThemeIconSelected_('default', theme)]]">
  </ntp-theme-icon>
  <dom-repeat id="themes" items="[[chromeThemes_]]">
    <template>
      <ntp-theme-icon title="[[item.label]]" on-click="onChromeThemeClick_"
          style="--ntp-theme-icon-frame-color:
              [[skColorToRgba_(item.colors.frame)]];
            --ntp-theme-icon-active-tab-color:
              [[skColorToRgba_(item.colors.activeTab)]];"
          tabindex="0"
          selected$="[[isThemeIconSelected_(item.id, theme)]]">
      </ntp-theme-icon>
    </template>
  </dom-repeat>
</ntp-grid>