zulip/static/styles/tooltips.css

[data-tippy-root] {
    /* Since tooltip elements are sometimes inside elements
     * which have different font-family, we force font-family
     * for tooltips here.
     */
    font-family: "Source Sans 3", sans-serif !important;
    word-wrap: break-word;

    /* Affects all tippy tooltips not using any theme. */
    .tippy-box:not([data-theme]) {
        background-color: hsl(0, 0%, 12%);

        &[data-placement^="top"] {
            > .tippy-arrow {
                &::before {
                    border-top-color: hsl(0, 0%, 12%);
                }
            }
        }

        &[data-placement^="bottom"] {
            > .tippy-arrow {
                &::before {
                    border-bottom-color: hsl(0, 0%, 12%);
                }
            }
        }

        &[data-placement^="left"] {
            > .tippy-arrow {
                &::before {
                    border-left-color: hsl(0, 0%, 12%);
                }
            }
        }

        &[data-placement^="right"] {
            > .tippy-arrow {
                &::before {
                    border-right-color: hsl(0, 0%, 12%);
                }
            }
        }
    }

    .tippy-content {
        font-size: 13px;
    }

    .tippy-arrow::before {
        /* `.tippy-arrow:before` element sometimes
         * inherits the height of the parent, we
         * don't want any height here since we
         * want it to remain an triangle.
         * The bug was only found in Firefox.
         */
        height: 0 !important;
    }
    /* If the text in the tooltips stretches to multiple lines,
     * we want the lines to be left-indented and not right-indented
     * by default.
     */
    text-align: left;
}