styles.css

.focus-mode .cm-s-obsidian div:not(.CodeMirror-activeline) > .CodeMirror-line {
    opacity: 0.85;
    filter: saturate(0.85);
}

.focus-mode div.view-header,
.focus-mode div.status-bar,
.focus-mode div.workspace-ribbon:not(.mod-left),
.focus-mode .workspace-split.maximised .workspace-leaf:not(.mod-active),
.focus-mode
    .workspace-split.maximised
    .workspace-leaf.mod-active
    ~ .workspace-split {
    display: none;
}

.focus-mode .view-content {
    height: 100%;
}

.focus-mode .workspace-split.maximised .workspace-leaf.mod-active {
    /* 4px is for scrollbar width: */
    flex-basis: calc(100% - 4px);
}

.focus-mode div.workspace-ribbon {
    visibility: hidden;
}

.focus-mode
    .side-dock-ribbon-action[aria-label="Toggle Focus Mode (Shift + Click to show active pane only)"] {
    visibility: visible;
}

/* Thanks to @AidenLx! */
/* Fixes for the Obsidian Tabs plugin: */
.focus-mode.plugin-tabs div.view-actions,
.focus-mode.plugin-tabs .stayopen div.view-header {
    display: none;
}

.focus-mode.plugin-tabs div.view-header {
    display: flex;
}