Template:OOOInfoBoxTabber/styles.css

/* OOO Infobox – Tabber wrapper
   - Default width matches .ooo-infobox (300px)
   - Tabs fill full width (equal columns)
   - Hides any separator line drawn by themes/extensions
*/

.ooo-infobox-tabwrap {
  float: right;
  clear: right;
  width: 300px;                 /* keep in sync with .ooo-infobox */
  margin: 0 0 1em 1em;
}

/* alignment overrides (set by module |align=...) */
.ooo-infobox-tabwrap--left   { float:left;  clear:left;  margin:0 1em 1em 0; }
.ooo-infobox-tabwrap--none   { float:none;                margin:0 0 1em 0; }
.ooo-infobox-tabwrap--center { float:none; display:block; margin:0 auto 1em; }

/* TAB STRIP — full-width equal tabs */
.ooo-infobox-tabwrap .tabber__tabs {
  display: flex;
  flex-wrap: nowrap;            /* keep in one row; change to wrap if you prefer */
  gap: .25rem;
  margin: 0 0 .5rem 0;
  width: 100%;
  box-sizing: border-box;
  border: 0;                    /* kill any normal border */
  background-image: none;       /* kill image-based lines */

  position: relative;           /* for the overlay below */
}

/* Overlay to MASK any stubborn baseline drawn by skins */
.ooo-infobox-tabwrap .tabber__tabs::after {
  content: "";
  position: absolute;
  left: 0; right: 0;
  bottom: -1px;                 /* sits on top of baseline */
  height: 2px;                  /* just enough to cover */
  background: var(--background-color-base, #ffffff); /* page bg (handles dark) */
}

/* Individual tabs – make them share the width equally */
.ooo-infobox-tabwrap .tabber__tab {
  flex: 1 1 0;
  min-width: 0;                 /* allow shrinking without overflow */
  text-align: center;

  display: inline-block;
  font-weight: 700;
  font-size: 90%;
  line-height: 1.2;
  white-space: normal;
  padding: .2rem .5rem;
  text-decoration: none;

  background: var(--background-color-neutral, #f5f5f5);
  color: var(--color-base, #202122);
  border: 1px solid #a2a9b1;    /* literal avoids TemplateStyles warnings */
  border-bottom: none;          /* blends into panel */
  border-radius: 6px 6px 0 0;
}

/* Active tab blends; slight overlap hides any seam with the panel */
.ooo-infobox-tabwrap .tabber__tab--active {
  background: var(--background-color-base, #ffffff);
  color: var(--color-base, #202122);
  margin-bottom: -1px;
}

/* Panels */
.ooo-infobox-tabwrap .tabber__panel {
  padding: 0;
  border: 0;
  background: transparent;
}

/* MOBILE */
@media (max-width: 640px) {
  .ooo-infobox-tabwrap,
  .ooo-infobox-tabwrap--left,
  .ooo-infobox-tabwrap--none,
  .ooo-infobox-tabwrap--center {
    float: none;
    width: 100%;
    margin: 0 0 1em 0;
  }

  /* on mobile you might prefer wrapping instead of equal-width squeeze: */
  .ooo-infobox-tabwrap .tabber__tabs { flex-wrap: wrap; }
  .ooo-infobox-tabwrap .tabber__tab { flex: 1 1 auto; }
}