Changes the readable line length in Obsidian Notes. Tested in Obsidian v0.14.6

obsidian-vii-adjustable-readable-line-length.css

/* Changes the readable line length in Obsidian Notes. Tested in Obsidian v0.14.6
See also: https://forum.obsidian.md/t/adjustable-readable-line-length/7564/6

Note: For this the "readable line length" property in settings has to be enabled
(as expected). 700px width is the application's default, adjust all numbers below. 

Pixel (or percentage) as a unit enables a width independent from the number of characters 
(good when adjusting zoom level / font size). For fixed amount of characters use  rem   */

/* Width in preview / read mode */
.markdown-preview-view.is-readable-line-width .markdown-preview-sizer, 
.markdown-source-view.is-readable-line-width .cm-content {
    max-width: 800px;
}

/* Widths in editor mode */
.markdown-source-view.mod-cm6.is-readable-line-width.is-rtl .cm-contentContainer {
    max-width: 800px;
    margin-left: auto;
    }

.markdown-source-view.mod-cm6.is-readable-line-width:not(.is-rtl) .cm-contentContainer {
    max-width: 800px; 
    margin-right: auto;
}

.markdown-source-view.mod-cm6.is-line-wrap.is-readable-line-width .cm-line:not(.HyperMD-table-row) {
    max-width: 800px;
}

.markdown-source-view.mod-cm6.is-line-wrap.is-readable-line-width .cm-content {
    max-width: 800px;
}